Many long‐lived plants are known to prolong dormancy in response to abiotic stresses such as drought. We are unaware, however, of any reports of plants prolonging dormancy in response to biotic stresses such as herbivory. We monitored 140 putative Solidago missouriensis clones (hereafter ‘clones’) ≥ 13 years before, during and after intense defoliation by the specialist herbivore Trirhabda canadensis. Eight of the clones produced no above‐ground growth in the season following defoliation. Though apparently killed, these clones reappeared 1–10 years after they disappeared, with six of them robustly recovering in a single season. We used 38 RAPD markers to test the hypotheses (denoted by H and numbered with subscripts) that territories were recovered by (H1) seedling establishment or (H2) rhizomes. We compared pre‐defoliation and post‐recovery genotypes in two clones using the same 38 markers. Our data document the existence of very large clones (60–350 m2 with c. 700–20 000 ramets), and support the hypothesis that recovery is from rhizomes. Within‐clone diversity is low, and the pre‐defoliation and post‐recovery genotypes match. We consider mechanisms that could enable plants entering dormancy with depleted resources to robustly recover, and the implications of dormancy for avoiding biotic stress such as that induced by T. canadensis.

Measures of molecular and morphological genetic variation are often used to set conservation priorities and design management strategies for plant taxa. Evaluated together they can give insights into a taxon's evolutionary status that neither data type alone can achieve. We investigated the distinctness and variability of Sedum integrifolium ssp. leedyi, a federally and state-listed taxon, from its conspecific relatives using 33 random amplified polymorphic DNA (RAPD) markers (253 plants) and 37 morphological characters from 1308 common-garden-grown plants. We included S. integrifolium ssp. leedyi (four populations), its conspecific relatives (11 populations), and S. rosea and S. rhodanthum populations in our study. The morphological and molecular data correspond in showing that S. integrifolium ssp. leedyi populations are highly distinct. However, the data sets differ in their estimates of the relatedness of some S. integrifolium ssp. leedyi populations and in the percentage variation detected due to differences among them (25 and 9-13% for the molecular and morphological data, respectively) suggesting little gene flow among populations and some differentiation, possibly from selective pressures. Given our data, we recommend that S. integrifolium ssp. leedyi merits protection under the U.S. Endangered Species Act and that its populations be managed as distinct units.

Information on reproduction and life history is important for the conservation of endangered plants. We investigated rates of flowering, seed set, and germination in populations of the endangered perennial plant Sedum integrifolium ssp. leedyi. Germination and flowering rates differed significantly among populations, but seed set rate did not. We assayed 26 plant clusters (81 stems) from four of the five known populations for evidence of clonal reproduction using 28 randomly amplified polymorphic DNA (RAPD) markers. Of the 81 stems, 75 had unique genotypes and three pairs had identical genotypes, suggesting that clonal reproduction is infrequent. Flowering, seed set, and germination rates were correlated with our estimates of ratios of effective to actual population sizes (Ne/N), but not with Ne. The single formally protected population may be experiencing inbreeding depression. We grew plants from seed to maturity in a greenhouse, with a germination rate of 77% and survival of 98% of the germinants at 6 mo, suggesting that this will be a viable means of ex situ propagation. Plants flowered 4-6 mo after germination and produced mature fruits 1-2 mo later, suggesting that they have the potential to sexually reproduce in their first or second season of growth.

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Taxa of Rhodiola L. (Crassulaceae) generally grow in arctic or alpine habitats. Some Rhodiola species are used medicinally, one taxon, Rhodiola integrifolia Raf. subsp. leedyi (Rosend. & J.W.Moore) Moran, (Leedy's roseroot), is rare and endangered, and the group's biogeography in North America is intriguing because of distributional disjunctions and the possibility that Rhodiola rhodantha (A.Gray) H.Jacobsen (2n = 7 II ) and Rhodiola rosea L. (2n = 11 II ) hybridized to form Rhodiola integrifolia Raf. (2n = 18 II ). Recent studies of the North American Rhodiola suggest that the group's current taxonomy is misleading. We analyzed nuclear and chloroplast DNA sequences (internal transcribed spacer (ITS), trnL intron, trnL-trnF spacer, trnS-trnG spacer) from the North American Rhodiola taxa. We combined our data with GenBank sequences from Asian Rhodiola species, performed parsimony, maximum likelihood (ML), and Bayesian phylogenetic analyses, and applied a Bayesian clock model to the ITS data. Our analyses reveal two major Rhodiola clades, suggest that hybridization between R. rhodantha and R. rosea lineages was possible, show two distinct clades within R. integrifolia, and demonstrate that a Black Hills, South Dakota, Rhodiola population should be reclassified as Leedy's roseroot. We recommend that R. integrifolia be revised, and that the Black Hills Leedy's roseroot population be managed as part of that rare and endangered taxon. Résumé : Le taxon des Rhodiola L. (Crassulaceae) croît normalement dans des habitats arctiques ou alpins. Certaines espèces de Rhodiola sont utilisées comme plantes médicinales et un taxon, Rhodiola integrifolia Raf. subsp. leedyi (Rosend. & J.W.Moore) Moran, (orpin de Leedy), est rare et menacé. La biogéographie de ce groupe en Amérique du Nord est intrigante à cause des disjonctions dans sa distribution et la possibilité que Rhodiola rhodantha (A.Gray) H.Jacobsen (2n = 7 II ) et Rhodiola rosea L. (2n = 11 II ) se soient hybridées pour former Rhodiola integrifolia Raf. (2n = 18 II ). Des études récentes réalisées sur Rhodiola d'Amérique du Nord suggèrent que la taxonomie actuelle de ce groupe est erronée. Les auteurs ont analysé les séquences d'ADN nucléaire et chloroplastique (espaceur transcrit interne (ETI), intron trnL, espaceur trnL-trnF, et espaceur trnS-trnG) du taxon des Rhodiola d'Amérique du Nord. Ils ont combiné leur données avec les séquences des espèces de Rhodiola d'Asie tirées de GenBank, réalisé des analyses phylogé-nétiques de parcimonie, par maximum de vraisemblance et bayésienne, et appliqué un modèle d'horloge moléculaire bayési-enne aux données de l'ETI. Leurs analyses révèlent l'existence de deux clades principaux de Rhodiola, suggèrent que l'hybridation entre les lignages R. rhodantha et R. rosea était possible, montrent l'existence de deux clades distincts à l'intérieur de R. integrifolia et démontrent qu'une population de Rhodiola de Black Hills, Dakota du Nord, devrait être re-classifiée en tant qu'orpin de Leedy. Ils recommandent que R. integrifolia soit révisé...