Opinion by Judge RICHARD C. TALLMAN; Concurrence by Judge NOONAN; Dissent by Judge TASHIMA.
OPINION
RICHARD C. TALLMAN, Circuit Judge.
Toby C. Patterson appeals his conviction and 188 month sentence for manufacturing 100 or more marijuana plants in violation of 21 U.S.C. § 841. Patterson contends that the district court violated the double jeopardy clause by vacating his guilty plea after it had been accepted. Patterson further alleges that the district court erred in denying his .motions to suppress and to exclude evidence regarding the number of marijuana plants, and in admitting expert testimony about the marijuana plants. Patterson claims that the district court erred when it failed to provide the jury with the option of basing its verdict on the weight of marijuana rather than on the number of plants. Patterson also argues that the evidence was insufficient to support the guilty verdict. Patterson urges us to hold that the career offender provisions of the Sentencing Guidelines and the mandatory minimum sentences of 21 U.S.C. § 841 violate the Eighth Amendment. Finally, Patterson asserts that the district court erred in denying his motion for a downward departure.
We have jurisdiction under 18 U.S.C. § 3742 and 28 U.S.C. § 1291, and we af-firip Patterson’s conviction and sentence on all grounds.
I
Detective Sergeant George Gow received information from a citizen named Calvin Stevens about marijuana growing on property near Stevens’ home in rural Bonner County, Idaho. Stevens told Gow that, while out for a walk, he noticed the strong smell of marijuana near a mobile home and saw pots of marijuana in a gated trailer on the property. Stevens informed Gow that he was familiar with the look and smell of marijuana since he had been “introduced to marijuana” in the Army. Stevens also stated that there was a humming noise coming from the trailer and that the trailer’s, windows seemed to be covered with plywood.
Stevens later met with Sergeant Gow and showed him the property at issue, although he did not actually take Gow onto the property. Sergeant Gow saw the trailer and heard the humming noise described by Stevens, a sound which Gow believed came from halogen grow lights that Gow had heard at other marijuana grow operations. After hearing Sergeant Cow’s testimony regarding his own observations, which corroborated the information provided by Stevens, a state magistrate judge found probable cause to issue a search warrant for the property.
Sergeant Gow and three other officers went to the property to execute the search warrant. They entered the trailer and found a number of marijuana plants growing in boxes inside. They pulled some of the smaller plants out of the boxes to take as evidence and cut some of the larger stalks that they were unable to remove. The officers videotaped this five-hour search and ultimately seized a total of 278 marijuana plants.
Patterson was indicted in August 1999 on one count of knowingly and intentionally manufacturing 100 or more marijuana [621]*621plants in violation of 21 U.S.C. §§ 841(a)(1) and (b)(1)(B). After initially entering a plea of not guilty, Patterson entered into a plea agreement on April 11, 2000, in which he agreed to plead guilty to manufacturing marijuana. The plea agreement stated that “the number of marijuana plants is in dispute, and the Defendant stipulates to no facts which relate to the number of marijuana plants.” The Plea Agreement further provided that this issue “will be litigated at sentencing,” which was scheduled for July 10, 2000. The Plea Agreement also provided that “the Court has not made any commitment relating to the appropriate sentence in this case, and is not bound by this agreement.” (emphasis in original).
The district court carefully conducted the Rule 11 colloquy when the plea was taken on April 4, 2000. The court reviewed the written provisions of the agreement with the defendant on the record and clarified the sole remaining issue in contention:
THE COURT: Now, as counsel has pointed out and stated here in open court, the number of plants is in dispute, and the Court is going to have to resolve that on the time of sentencing, based upon the evidence as presented; that is in accordance with your understanding?
THE DEFENDANT: Yes, Your Honor. ‡ ‡ ‡ ‡ ‡" ‡
THE COURT: [I]t is your position and your understanding that the Court has not made any commitment. relating to the appropriate sentence in this case and is not bound by the plea negotiations?
THE DEFENDANT: Yes, I understand.
THE COURT: Because the number of plants has not been determined, neither this Court nor counsel nor anyone else could tell you what the sentence might be at this point?
THE DEFENDANT: Yes, I understand that, Your Honor.
THE COURT: It is my understanding that you do admit that you are responsible or guilty of manufacturing marijuana plants and that you are guilty of the elements of this particular charge as outlined by Mr. McHugh [the prosecutor], but that you remain silent or not admitting the number of marijuana plants; is that correct?
THE DEFENDANT: That is correct, Your Honor.
THE COURT: So again,.other than not admitting to the number of marijuana plants, do you agree with the summary given by Mr. McHugh?
.THE DEFENDANT: Yes, I do, Your Honor.
THE COURT: So you admit those facts and agree that those facts sustain each element of the charge with the exception .of whether it be a class B, C or D felony, that will have to be determined once the Court determines.the number of plants; right?
THE DEFENDANT: Yes, sir.
Subsequently, on June 26, 2000, the United* States Supreme Court decided Apprendi v. New Jersey, 530 U.S. 466, 490, 120 S.Ct. 2348, 147 L.Ed.2d 435 (2000), which held that any fact, other than a prior conviction, that increases, the penalty for a crime beyond the statutory maximum, must be submitted to a jury and proven beyond a reasonable doubt. Patterson filed various objections to the Pre Sentence Report (“PSR”). The government filed a response to Patterson’s objections arguing, inter alia, that the guilty plea should be set aside as insufficient under Apprendi because Patterson was not informed of the number of marijuana plants at the time he pled guilty. At the July 10, 2000, hearing, [622]*622the district court agreed that the plea was invalid because the number of marijuana plants was not stipulated to by Patterson, nor found by a jury beyond a reasonable doubt. The court therefore vacated the guilty plea and scheduled a jury trial for September 2000.
Prior to trial, the district court denied Patterson’s motions to suppress evidence, concluding that the search warrant was supported by probable cause. The court also denied Patterson’s motion to exclude videotaped evidence regarding the number of plants, reasoning that Patterson was not unduly prejudiced by the police officers’ failure to preserve the pots in which the plants grew. Finally, the court granted Patterson’s unopposed motion to weigh the marijuana prior to trial.
The case proceeded to trial over Patterson’s objection. The jury found Patterson guilty of manufacturing marijuana. It returned a Special Verdict announcing, “We find the Defendant, Toby C. Patterson, knowingly and intentionally manufactured the following quantity of marijuana: One-hundred (100) or more marijuana plants.” The district court sentenced Patterson to a term of 188 months’ imprisonment and five ; years’ supervised release. Patterson timely appealed.
II
Patterson contends that because jeopardy attached when the court accepted his guilty plea, the double jeopardy clause was violated when the district court vacated’ his guilty plea and proceeded to trial. Double jeopardy claims are reviewed de novo. See United States v. Byrne, 203 F.3d 671, 673 (9th Cir.), cert. denied, 531 U.S. 1114, 121 S.Ct. 861, 148 L.Ed.2d 774 (2001). Whether the district court is required to enforce a plea agreement is a question of law we review de novo. See United States v. Fagan, 996 F.2d 1009, 1013 (9th Cir.1993). We conclude that because the court conditionally accepted Patterson’s plea, jeopardy did not attach, and Patterson was not twice placed in jeopardy for the same offense.
A
The plea agreement in the instant case provided that the parties did not agree on the sentence, that the court made no commitment about the sentence, and that it was not bound by the agreement. The agreement also stated that the number of marijuana plants would be litigated at sentencing and that Patterson was aware of the varying penalties under 21 U.S.C. § 841(b)(1) for different quantities of plants.
Rule 11(c) of the Federal Rules of Criminal Procedure requires that the district court determine that the defendant understands “the nature of the charge to which the plea is offered” before the court accepts a guilty plea. Fed.R.Crim.P. 11(c). During the thorough Rule 11 colloquy, the district judge told Patterson that if, “after considering the presentence report and any other evidence that, it might have that something other than what was being recommended should be imposed, the Court can do that.” The court further stated that it had “not made any commitment relating to the appropriate sentence in this case and is not bound by the plea negotiations.” After finding that the plea was knowing and voluntary, and that there was a factual basis for each of the elements of the offense, the court accepted the plea, set the date for sentencing, and told Patterson about the PSR that was to be prepared. Finally, the court reminded Patterson that it would “take everything into consideration right up to the day of sentencing.”
[623]*623Before Patterson’s sentencing date arrived, the Supreme Court decided Appren-di. In light of this decision, the district court, on the government’s motion, chose to vacate defendant’s plea and gave him the option of either negotiating a new plea agreement or going to trial. As the district court noted, all parties had proceeded on the assumption that the number of plants at issue did not have to be proven beyond a reasonable doubt before a jury and this assumption was no longer valid in light of Apprendi
Based upon the original Indictment in this case, the terms of his Plea Agreement, and the defendant’s colloquy with the court when he entered his plea of guilty, it is clear that Patterson was not twice placed in jeopardy for the same offense. Patterson was convicted only one time, by a jury; of the crime of manufacturing 100 or more marijuana plants in violation of 21 U.S.C. §§ 841(a)(1) and (b)(1)(b), punishable by 5 to 40 years’ imprisonment. While the parties were understandably uncertain as to how they should proceed in light of Ap-prendi the district court did not err in vacating the plea and submitting the quantity issue to the jury as the Supreme Court now commands. At all times throughout this single prosecution Patterson faced the same crime, with the same potential penalties, for which he was ultimately tried by a jury, convicted, and sentenced.
The district court vacated Patterson’s plea based upon the government’s understandable post-Apprendi argument that Patterson had never pled to a third “element,” the quantity of marijuana involved in his offense. But as we have now clarified, “Apprendi eschews the distinction between sentencing factors and elements of a crime: ‘the relevant inquiry is one not of form, but of effect — does the required finding expose the defendant to a greater punishment than that authorized by the jury’s guilty verdict?’ ” United States v. Buckland, 277 F.3d 1173, 1180 (9th Cir.2002) (en banc) (emphasis in original) (citing Ap-prendi 530 U.S. at 494, 120 S.Ct. 2348). The answer in regard to Patterson is plainly no.
Patterson’s reliance on United States v. Nordby, 225 F.3d 1053 (9th Cir.2000), overruled in part by Buckland, 277 F.3d at 1182, is also unavailing. Patterson argues that since he only pled guilty to the manufacture of an unspecified amount of marijuana, the maximum sentence that he could have received under § 841 was five years. In Nordby, 225 F.3d at 1056, a panel of this court vacated and remanded a sentence where the issue of drug quantity, “a fact that increases the prescribed statutory maximum penalty to which a criminal defendant is exposed,” had not been submitted to a jury and proven beyond a reasonable doubt. The court directed that, in light of Apprendi Nordby’s sentence could “not [] exceed the statutory maximum applicable to the facts as found by the jury beyond a reasonable doubt.” Id.
Unlike the defendant in Nordby, Patterson’s sentence did not exceed the “statutory maximum applicable to the facts found by the jury beyond a reasonable doubt.” Patterson’s conviction and sentence were not based on his conditional plea of guilty to an unspecified amount of marijuana. Rather, they were based on a finding by a jury that Patterson was guilty of manufacturing 100 or more marijuana plants. The issue of drug quantity was submitted to and decided by a jury beyond a reasonable doubt. Thus, Patterson’s conviction and sentence fit squarely within the rule enunciated by the Supreme Court in Apprendi, acknowledged in Nordby, and recently, clarified by our en banc panel in Buckland. To the extent that Nordby relied on the distinction between sentencing factors and [624]*624elements in making its determination, it was overruled by Buckland. See 277 F.3d at 1182.
B
While it is true that “[jjeopardy ordinarily attaches upon the court’s acceptance of a plea agreement,” United States v. Smith, 912 F.2d 322, 324 .(9th Cir.1990), a guilty plea that is only conditionally accepted does not give rise to jeopardy. See United States v. Cordova-Perez, 65 F.3d 1552, 1557 (9th Cir.1995); see also 21 AM. JUR.2d Criminal Law § 337 (1998).
In Cordova-Perez, 65 F.3d at 1553, the defendant pled guilty to a lesser related offense in exchange for the government’s promise to move for dismissal of other charges. ' The district court rejected the agreement after viewing the PSR on the basis that the agreement did not adequately reflect the seriousness of the defendant’s offense behavior. Id. at 1554. We held that the district court’s acceptance of the guilty plea was “impliedly contingent” upon its review of the PSR, and that the court therefore retained discretion to reject the plea based on information it subsequently learned from the PSR. See id. at 1555. We concluded that the district court’s acceptance of the guilty plea was conditional and therefore. rejected defendant’s double jeopardy claim, since jeopardy did not attach upon “acceptance” of the conditional plea. See id. at 1557.
The district court’s acceptance of Patterson’s guilty plea here was likewise conditional. The district court told Patterson that if, “after considering the presentence report and any other evidence that it might have that something other than what was being recommended should be imposed, the Court can do that.” The court retained discretion to reject the plea agreement on the basis of information it gained from either the PSR or on the basis of any other evidence that would indicate that the plea agreement was improper. In deciding that the plea agreement that had been entered into did not reflect the law as enunciated by the Supreme Court in Ap-prendi, the district court properly exercised its discretion.
At no time did anyone involved in these proceedings stipulate to the quantity that would determine the sentence Patterson ultimately faced. While it was true that everyone at entry of the plea expected the judge to make that factual determination at sentencing, we see no prejudice to Patterson in later having the jury do it since the law had changed in the interim. The possibility that the court might set aside the guilty plea because the governing law has changed “is a risk inherent in the bargain a defendant makes when he agrees to the court’s conditional acceptance of his guilty plea. Here, that acceptance was conditional.” See Cordova-Perez, 65 F.3d at 1556. Therefore, jeopardy did not attach upon the court’s acceptance of the plea.1
[625]*625Further, while we have held that a district court is without authority to vacate an “unconditionally accepted” plea, see United States v. Partida-Parra, 859 F.2d 629, 631 (9th Cir.1988), the conditional nature of the court’s acceptance of the guilty plea here distinguishes this case from Partida-Parra. See also Cordova-Perez, 65 F.3d at 1555 n. 5 (noting that conditional nature of court’s acceptance of the plea distinguished Cordova-Perez’s case from Parti-das-Parra). Thus, the district court did not err in vacating Patterson’s conditional plea in light of Apprendi.
“The Fifth Amendment’s prohibition against placing a defendant ‘twice in jeopardy” represents a constitutional policy of finality for the defendant’s benefit in federal criminal proceedings.” United States v. Jorn, 400 U.S. 470, 479, 91 S.Ct. 547, 27 L.Ed.2d 543 (1971). That policy has not been offended in this case. Patterson has not been subjected to the harassment of successive prosecutions and there is no question of multiple trials or multiple punishments. Because the judge clearly stated that he was ■ not bound by the plea agreement or plea negotiations, he had the right to vacate the plea in light of the change in the law of sentencing as to who would make the .quantity determination and by what standard of proof as enunciated by the Supreme Court in Apprendi.2
The court’s acceptance of Patterson’s guilty plea was conditional and jeopardy did not attach. See Cordova-Perez, 65 F.3d at 1557; United States v. Sanchez, 609 F.2d 761, 763 (5th Cir.1980). Accordingly, there was no double jeopardy violation in this case.- Vacating the plea in order to submit the quantity issue to the jury was not error.
Ill
Patterson contends that the district court erred in denying his motion to suppress the evidence found as a result of the.search because the search warrant was not supported by probable cause. We review the district court’s denial of a motion to suppress evidence seized in a search de novo. See United States v. Murillo, 255 F.3d 1169, 1174 (9th Cir.2001), cert. denied, - U.S. -, 122 S.Ct. 1342, 152 L.Ed.2d 245 (2002). The factual findings underlying that decision are reviewed for clear error. See id. The magistrate judge’s finding of probable cause is therefore reviewed for clear error and is accorded significant deference. See United States v. Hay, 231 F.3d 630, 634 n. 4 (9th Cir.2000), cert. denied, — U.S. -, 122 S.Ct. 135, 151 L.Ed.2d 88 (2001).
In determining whether probable cause supported the issuance of a search warrant in this case, we must determine whether there was a substantial basis for the magistrate’s finding of probable cause. See Illinois v. Gates, 462 U.S. 213, 239, 103 S.Ct. 2317, 76 L.Ed.2d 527 (1983). The [626]*626magistrate’s task is “to make a practical, common-sense decision,” given the totality of the circumstances. See id. at 238, 103 S.Ct. 2317. The magistrate is entitled to rely upon the law enforcement officer’s training and experience when evaluating the information related to him in the determination of probable cause. See United States v. Gil, 58 F.3d 1414, 1418 (9th Cir.1995).
■ Patterson does not establish that the magistrate clearly erred in finding probable cause to issue the search warrant. ■ On the contrary, the totality of the circumstances justified a finding of probable cause in this case.
Sergeant Gow testified that Stevens described a gutted trailer containing pots of marijuana, that Stevens saw and smelled marijuana on the property, and that Stevens heard a humming noise coming from the trailer. Sergeant Gow further testified that his own observations while at the property confirmed this information, including the smell of marijuana and the humming noise, which was similar to what Gow had heard at other marijuana operations.
Sergeant Gow also testified as to his own law enforcement experience. Gow stated that he had been assigned to the drug task force for eight years and that he had investigated numerous marijuana growing operations, including serving search warrants at over twenty-five such operations. As to Stevens’ reliability, Sergeant Gow testified that he had known Stevens for eighteen years and that Stevens had been introduced to marijuana in the Army and was therefore familiar with the appearance and smell of marijuana.
Given the totality of the circumstances, and the significant deference attached to the magistrate’s determination of probable cause, the magistrate did not clearly err in determining that Sergeant Govifs testimony was sufficient to support a finding of probable cause. See id. We therefore affirm the district court’s denial of Patterson’s motion to suppress.
IV
Patterson contends that because the government destroyed the pots in which the marijuana grew, which he claims constituted the only evidence of whether the plants had roots, the district court erred in denying his motion to exclude evidence about the number of marijuana plants. Patterson further contends that the destruction of the evidence violated his “constitutional right of access to evidence” under the Due Process Clause. See United States v. Belden, 957 F.2d 671, 673 (9th Cir.1992).
We review for an abuse of discretion the district court’s decision whether to exclude evidence as a sanction for destrojdng or failing to preserve evidence. See id. at 674. The district court’s determination of whether the government’s failure to preserve potentially exculpatory evidence violated a defendant’s due process rights is reviewed de novo. See United States v. Cooper, 983 F.2d 928, 931 (9th Cir.1993).
As an initial matter, Patterson contends that without the roots of the plants, there is no evidence of the number of plants, and so the only evidence of the amount of marijuana is its weight. Patterson’s argument is based on the requirement that there must be “readily observable evidence of root formation” in order for a marijuana plant to be counted as a plant for sentencing purposes. See United States v. Robinson, 35 F.3d 442, 446 (9th Cir.1994). Patterson asserts that the de[627]*627struction of the pots containing the roots has made it impossible to determine whether or not the plants had roots, and that, accordingly, there is no evidence of the number of marijuana plants. This assertion is erroneous.
Sergeant Gow testified that the plants that he counted did have roots. Gow further testified about his training and experience in differentiating between different stages of plant growth. He specifically stated that when he counted the plants in Patterson’s operation he did not include any plants that he thought did not have roots. In addition, the video of the search also provides sufficient evidence of the number of marijuana plants found. Therefore, Patterson’s claim is unpersuasive that the only proper evidence of the amount of marijuana in this case is its weight.
Patterson argues that because the roots of the plants were not preserved by the government, the district court erred in allowing the government to present other evidence about the number of marijuana plants. Factors to be considered in determining whether evidence should be excluded as a sanction for government destruction of, or failure to preserve, evidence are the quality of the government’s conduct and the degree of prejudice to the defendant. See Belden, 957 F.2d at 674. The nature and degree of participation by the federal government and its attorneys in the loss or destruction of the evidence is also a consideration. See id.
In evaluating the quality of the government’s conduct, the district court found that the police officers’ decision not to preserve the roots of the plants did not constitute bad faith, but was instead based on their reasoning that the plants were clearly healthy and viable. The district court also found that Patterson was not unduly prejudiced by the destruction of the pots containing the roots because he had access to the video of the search and would have the opportunity to cross-examine the officers who counted the plants. See id. The court also noted that it was state not federal authorities who collected and stored the evidence. See id. Based on these facts, the district’s court decision not to exclude evidence of the number of marijuana plants was not an abuse of discretion. The district court’s denial of Patterson’s motion to exclude is therefore affirmed.
C •
Patterson also contends that the government’s failure to preserve the roots violated his due process rights. “[U]nless a criminal defendant can show bad faith on the part of the police, failure to preserve potentially useful evidence does not constitute a denial of due process of law.” Arizona v. Youngblood, 488 U.S. 51, 58, 109 S.Ct. 333, 102 L.Ed.2d 281 (1988); United States v. Rambo, 74 F.3d 948, 954 (9th Cir.1996).
Patterson has neither argued nor presented any evidence that the officers acted in bad faith in failing to preserve the roots. “Indeed, he does not even challenge thd district court’s finding that the government'did not act in bad faith” in not preserving the roots. United States v. Hernandez, 109 F.3d 1450, 1455 (9th Cir.1997). Patterson’s due process claims can be rejected on this basis alone. See Youngblood, 488 U.S. at 58, 109 S.Ct. 333 (holding that failure to preserve potentially useful evidence does not violate due process-absent a showing of bad faith); Hernandez, 109 F.3d at 1455 (finding no due process violation where there was no evidence of bad faith); Rambo, 74 F.3d at 954 [628]*628(rejecting due process claim because deputies’ conduct indicated “only poor judgment, not bad faith”).
Even if Patterson could demonstrate bad faith, m order for the due process clause to be implicated, the evidence that was lost “must both possess an exculpatory value that was apparent before the evidence was destroyed, and be of such a nature that the defendant would be unable to obtain comparable evidence by other reasonably available means.” California v. Trombetta, 467 U.S. 479, 489, 104 S.Ct. 2528, 81 L.Ed.2d 413 (1984); Hernandez, 109 F.3d at 1455. Patterson has not shown that the evidence at issue satisfies either of these conditions.
Y
Patterson argues that the district court erred in admitting expert testimony by a horticulturalist, Professor Danny L. Barney, regarding whether the plants he saw in the police video had root formations. Patterson argues that whether the video showed roots on the marijuana plants is a jury determination. Patterson also contends that Barney was not qualified as an expert on marijuana.
We review the district court’s decision to admit expert testimony for an abuse of discretion. See United States v. Alatorre, 222 F.3d 1098, 1100 (9th Cir. 2000); United States v. Hankey, 203 F.3d 1160, 1167 (9th Cir.), cert. denied, 530 U.S. 1268, 120 S.Ct. 2733, 147 L.Ed.2d 995 (2000). Because the district court is given broad discretion in deciding whether to admit expert testimony, its ruling may be reversed only if “manifestly erroneous.” Hankey, 203 F.3d at 1167 (internal quotations omitted).
The government called Professor Barney, a “plant physiologist” who described himself as having worked extensively with plant propagation, to testify about whether the marijuana plants seen in the police video had root systems and thus were “established plants ... capable of independent survival.” Barney testified that, although he had never worked with marijuana plants, developmental characteristics such as size, wilting, discoloration, or new shoot growth, were common to many plants. Barney told the jury that all but one of the plants that he saw Sergeant Gow cutting and counting on the video had root systems.
The district court concluded that Professor Barney’s testimony could assist the jury in - determining whether the plants were actually plants or merely cuttings. The court further stated that, although Barney had no experience with marijuana plants, he did testify about the common characteristics of plants. Reasoning that Barney’s experience went to the weight to be given his testimony rather than to its admissibility, the court decided that it would be for the jury to decide whether Barney’s testimony was credible.
Federal Rule of Evidence 702 provides:
If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training or education, may testify thereto in the form of an opinion or otherwise.
“In determining whether expert testimony is admissible under Rule 702, the district court must keep in mind Rule 702’s ‘broad [629]*629parameters of reliability, relevancy, and assistance to the trier of fact.’ ” Sementilli v. Trinidad Corp., 155 F.3d 1130, 1134 (9th Cir.1998) (quoting Desrosiers v. Flight Int’l of Fla., 156 F.3d 952, 960-61 (9th Cir.1998)).
The district court’s decision to admit Professor Barney’s testimony was not “manifestly erroneous,” and did not constitute an abuse of discretion. Hankey, 203 F.3d at 1167. In Robinson, we adopted the rule that marijuana cuttings are not plants for sentencing purposes unless there is “readily observable evidence of root formation.” 35 F.3d at 446 (internal quotations omitted). We noted that “requiring readily observable evidence of root formation is a common-sense approach that will prevent the costly and confusing battle of botanical experts which occurred in this case.” Id. (internal quotations omitted). However, we did not hold that expert testimony regarding root formation is impermissible.
The testimony in Robinson likely focused on the issue of when a plant actually becomes a plant, an inquiry which would require a considerable amount of expert testimony. See id. Here, the issue before the jury was whether the marijuana plants seized actually had roots so as to be classified as “plants” for sentencing purposes. Whether a plant actually has roots, and thus meets the definition of a plant for sentencing purposes, is a question whose determination could be aided by expert botanical testimony such as that presented in this case.
Professor Barney testified that the plants that Sergeant Gow cut and counted most likely had root systems because they were healthy, vigorous, and did not show signs of “wilting such as you would see if you had simply taken a cutting and stuck in into the soil.” He distinguished those from other plants seen in the video that he thought were cuttings, based on the lack of new growth and dead plant tissue. ■ Barney gave his opinion as to whether the plants had roots, but he also described for the jury the plant characteristics that helped him make that determination. This information about plant growth was relevant and helpful to the ultimate question before the .jury, which was free to accept or reject his ultimate conclusion. See Fed. R.Evid. 704(a) (“testimony in the form of an opinion or inference otherwise admissible is not objectionable because it embraces an ultimate issue to be decided by the trier of fact”).
The district court did not manifestly err in concluding that this type of information would assist the jury in determining the number of plants for sentencing purposes, and therefore did not abuse its discretion in admitting the testimony. It properly exercised its “gatekeeping” function under Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993).
VI
Patterson contends that the district court erred in failing to instruct the jury that it had the option of basing its verdict on the weight of the marijuana, rather than on the number of plants, and in failing to include that option on the verdict form. Jury instructions are reviewed as a whole to determine whether they are misleading or inadequate to guide the jury’s deliberation. See United States v. Dixon, 201 F.3d 1223, 1230 (9th Cir. 2000). Whether the instructions adequately presented the defendant’s theory of the case is reviewed de novo, but if the instructions fairly and adequately covered the elements of the offense, we review the instructions’ “precise formulation” for an abuse of discretion. Id. (internal quotations omitted). Whether a jury instruction mis[630]*630states the elements of a statutory crime is reviewed de novo. See Vallejo, 237 F.3d at 1024. The district court’s decision to use a special verdict form over a defendant’s objection is reviewed for an abuse of discretion. See United States v. Reed, 147 F.3d 1178, 1180 (9th Cir.1998).
Patterson stipulated to “knowingly and intentionally manufactur[ing] marijuana.” When a defendant’s offense involves the growing of marijuana, the drug quantity is determined using the equivalency ratio in § 2D1.1 of the United States Sentencing Guidelines, which is based on the number of plants.3 See United States v. Wegner, 46 F.3d 924, 928 (9th Cir.1995) (stating that “[w]hen sufficient evidence establishes that defendant actually grew and was in possession of live plants, then conviction and sentencing can be based on evidence of live plants”). The drug quantity is based on the number of plants regardless of whether the plants were actually seized or not. See id. at 926-28. Patterson’s offense involved marijuana plants, not harvested marijuana; he was therefore properly sentenced according to the number of plants rather than the weight of the marijuana.
Although the district court declined to present Patterson’s theory of the case to the jury, no authority supports his claim that he should be sentenced according to the weight of the marijuana, rather than the number of plants. See United States v. Mason, 902 F.2d 1434, 1438 (9th Cir.1990) (holding that a defendant is only entitled to a jury instruction on his theory of defense if his theory is supported by the law and has some foundation in the evidence). The district court’s jury instruction correctly directed the jury to determine the number of plants attributable to Patterson, rather than the weight. Its decision not to give them the option of considering weight on the special verdict form did not constitute an abuse of discretion and is therefore affirmed.
VII
Patterson contends that because there was no reliable evidence that any plants existed, the evidence was insufficient to support the verdict. There is sufficient evidence to support a conviction if, viewing the evidence in the light most favorable to the government, any rational trier of fact could have found the essential elements of the crime beyond a reasonable doubt. See United States v. Wright, 215 F.3d 1020, 1025 (9th Cir.), cert. denied, 531 U.S. 969, 121 S.Ct. 406, 148 L.Ed.2d 313 (2000).
The police video of the search and Sergeant Gov/s testimony constitute sufficient evidence - for a rational jury to find that Patterson grew marijuana plants, and that they were plants with root systems. Patterson’s claim that there was insufficient evidence to support the verdict has no merit.
VIII
Patterson argues that the career offender provisions of § 4B1.1 of the United States Sentencing Guidelines and the mandatory minimum sentencing provisions of 21 U.S.C. § 841 violate due process, equal protection, and the Eighth Amendment. Patterson further contends that the disparity between the treatment of marijuana manufacturers and those who merely possess or distribute marijuana is [631]*631arbitrary, and that the equivalency ratio, requiring him to be sentenced according to the number of marijuana plants, is irrational. The constitutionality of a sentence is reviewed de novo. See United States v. Reyes-Pacheco, 248 F.3d 942, 945 (9th Cir. 2001).
In determining whether a sentence violates the Eighth Amendment, we must accord “substantial deference” to legislative determinations of appropriate punishments. See Harmelin v. Michigan, 501 U.S. 957, 998-99, 111 S.Ct. 2680, 115 L.Ed.2d 836 (1991) (citing Solem v. Helm, 463 U.S. 277, 290, 103 S.Ct. 3001, 77 L.Ed.2d 637 (1983)). Although the Eighth Amendment does not require “strict proportionality between crime and sentence,” it “forbids ... extreme sentences that are ‘grossly disproportionate’ to the crime.” Harmelin, 501 U.S. at 1001, 111 S.Ct. 2680 (citing Solem, 463 U.S. at 288, 303, 103 S.Ct. 3001).
Patterson contends that application of the career offender provisions of § 4B1.1 of the Sentencing Guidelines to his case,4 resulting in an increased sentencing range, violates due process, equal protection, and the Eighth Amendment.
In United States v. Carr, 56 F.3d 38, 39 (9th Cir.1995), the defendant claimed that application of § 4B1.1 resulted in a sentence grossly disproportionate to the seriousness of his prior offenses, thus violating the Eighth Amendment and the Due Process Clause. Carr was convicted of possession with intent to distribute 66.92 grams of cocaine base. Because of two prior felony controlled substance convictions, Carr’s sentence was enhanced pursuant to § 4B1.1 to 262 months. Since the defendant’s sentence was less severe relative to his offenses than other sentences upheld by the Supreme Court, we held that an Eighth Amendment challenge to his sentence was foreclosed by Supreme Court precedent. See id. Further, we rejected the defendant’s contention that § 4B1.1 violates due process; See id.
Patterson’s claim that application of the career offender provisions of § 4B1.1 in his case resulted in an arbitrary and disproportionate sentence must likewise be rejected. “Generally, as long as the sentence imposed on a defendant does not exceed statutory limits, this court will not overturn it on Eighth Amendment grounds.” United States v. Parker, 241 F.3d 1114, 1117 (9th Cir.2001).
Nevertheless, we evaluate the constitutionality of the sentence under the Eighth Amendment by considering three factors: (1) the gravity of the offense and harshness of the penalty, (2) the sentences imposed oh other criminals in the same jurisdiction, and (3) the sentences imposed for commission of the sanie crime in other jurisdictions. See Solem, 463 U.S. at 292, 103 S.Ct. 3001. Under the circumstances [632]*632of this case, we cannot say that Patterson’s sentence was “so disproportionate to the gravity of his offenses as to violate the Eighth Amendment.” Carr, 56 F.3d at 39.
Patterson was sentenced to 188 months’ imprisonment for manufacturing 100 or more marijuana plants, the minimum of his sentencing guideline range of 188 to 235 months. Further, the 188-month sentence was well within the statutory maximum applicable to him, 40 years. See 21 U.S.C. § 841(b)(1)(B). Considering the gravity of the offense in this case, manufacturing 100 or more marijuana plants, and the fact that the penalty imposed was both at the minimum of the Guideline range and well below the statutory maximum, we cannot say that Patterson’s sentence was “grossly disproportionate” to his crime.
Further, for crimes “classified and classifiable as felonies[,] ... the length of the sentence actually imposed is purely a matter of legislative prerogative.” Rummel v. Estelle, 445 U.S. 263, 274, 100 S.Ct. 1133, 63 L.Ed.2d 382 (1980); Harmelin, 501 U.S. at 998, 111 S.Ct. 2680 (noting that sentencing laws involve “substantive peno-logical judgment that, as a general matter, is properly within the province of legislatures, not courts”) (internal quotations omitted). There is no reason why the legislature’s determination of sentences for felonies committed by career offenders should be accorded less deference here where the sentence is not grossly disproportionate to the crime.
We also reject Patterson’s due process challenge to § 4B1.1. This court has repeatedly determined that the Guidelines do not unduly limit the. sentencing court’s discretion ■ to individualize a defendant’s sentence, and thus do not violate substantive or procedural due process. See, e.g., United States v. Brady, 895 F.2d 538 (9th Cir.1990); United States v. Jones, 907 F.2d 929, 930 (9th Cir.1990); Carr, 56 F.3d at 39. Section 4B1.1 does not operate in contravention of due process either on its face or as applied in this case. See Carr, 56 F.3d at 39.
In rejecting Eighth Amendment claims regarding ■ mandatory consecutive minimum sentences imposed under 18 U.S.C. § 924(c), we have stated that “[generally, as long as the sentence imposed on a defendant does not exceed statutory limits, this court will not overturn it on Eighth Amendment grounds.” Parker, 241 F.3d at 1117. Patterson’s sentence is within the statutory limits of § 841, whose mandatory minimum sentences have long been upheld against Eighth Amendment challenges. See, e.g., United States v. Kidder, 869 F.2d 1328, 1334-34 (9th Cir.1989). Moreover, Patterson’s sentence was not so “grossly disproportionate” to the crime so as to violate the Eighth Amendment. See Harmelin, 501 U.S. at 1001, 111 S.Ct. 2680.
C
Patterson’s challenges to the disparity between sentences for marijuana growers and marijuana distributors and to the equivalency ratio have also been rejected by this court. See Belden, 957 F.2d at 676 (reasoning that § 2D1.1 is rationally based on the “recognition of a higher- level of culpability for marijuana growers compared to those who merely possess the harvested product”); see also Wegner, 46 F.3d at 926 (addressing the pre-1995 version of the Guidelines, noting that Congress’ intent with regard to § 2D1.1 was to “punish the manufacture of marijuana more severely”). Patterson’s challenges under the Eighth Amendment are therefore without merit.
[633]*633IX
Patterson contends that the district court did not adequately consider his motions for departure. Unless a district court’s refusal to depart downward is based on its conclusion that it lacks the authority to depart, a district court’s discretionary refusal to depart downward from the Sentencing Guidelines is not reviewable on appeal. See United States v. Tam, 240 F.3d 797, 805 (9th Cir.2001). Whether a district court has adequately stated the reasons for a sentence is a question of law and is reviewed dé novo. See United States v. Upshaw, 918 F.2d 789, 792 (9th Cir.1990).
The record in this ease clearly indicates that the district court’s refusal to depart from the Guidelines was not based on its conclusion that it lacked the authority to depart. Rather, it was based on its own investigation of Patterson’s history as well as on the findings in the. PSR, which the court adopted as its own. Thus, on appeal we may not review the district court’s discretionary refusal to depart downward from the Guidelines.
X
Patterson’s conviction and sentence áre AFFIRMED.