Penstemon miniatus (Scrophulariaceae): New combinations

Penstemon apateticus Straw is found to be synonymous withP. miniatus Lindl.Penstemon miniatus subsp.apateticus andP. miniatus subsp.townsendianus are presented as new combinations. *** DIRECT SUPPORT *** A01CT127 00005     

Diploid hybrid speciation in Penstemon (Scrophulariaceae) revisited

Diploid hybrid speciation remains a central issue in plant evolutionary biology. Here we test hypotheses of diploid hybrid speciation and introgressive hybridization in Penstemon section Peltanthera where P. spectabilis is a purported hybrid derivative species of the progenitors P. centranthifolius and P. grinnellii, and P. clevelandii is regarded as a hybrid derivative of P. centranthifolius and P. spectabilis. Forty-five populations representing P. centranthifolius (subsection Centranthifolii); P. spectabilis, P. clevelandii, P. grinnellii, P. palmeri in subsection Spectabiles; and P. × parishii (a purported hybrid between P. centranthifolius and P. spectabilis) were examined for allozyme differentiation. Penstemon centranthifolius has high-frequency allozymes at seven isozyme loci that differentiate it from species in subsection Spectabiles, whereas no genetic markers are detected that reliably differentiate species within Spectabiles. Because our data reveal that P. centranthifolius is genetically distinct compared to species in Spectabiles, we conclude that a recent hybrid origin of P. spectabilis and P. clevelandii with P. centranthifolius as a progenitor is not supported. Bidirectional gene flow and introgression between P. centranthifolius and species of subsection Spectabiles is indicated, however, based on the low-frequency occurrence of P. centranthifolius marker alleles in species of Spectabiles and of Spectabiles marker alleles in P. centranthifolius in areas of sympatry.     

A new Penstemon (Scrophulariaceae) from northwestern Nevada

Penstemon floribundus, belonging to sect.Saccanthera (Benth.) A. Gray and known only from the western edge of the Jackson Mountains, Humboldt Co., Nevada, is described, illustrated, and discussed.     

A new Penstemon (Scrophulariaceae) from northwestern Arizona

Penstemon distans, belonging to sect.Cristati (Rydb.) Pennell and known only from the southeastern edge of the Shivwits Plateau, Mohave Co., Arizona, is described, illustrated and discussed.     

Subgeneric and sectional names for Intermountain Penstemon (Scrophulariaceae)

Some of the earliest validly published subgeneric and sectional names forPenstemon that have been overlooked or disregarded in recent years are recalled. Lectotype species are designated for sectionsGentianoides G. Don andSaccanthera Benth.     

Dynamic nectar replenishment in flowers of Penstemon (Scrophulariaceae)

Plants that experience variation in pollinator visitation rates or fluctuations in weather conditions may be expected to have evolved homeostatic mechanisms that regulate their nectar offerings, thereby providing a more constant reward to the pollinators. A limited degree of such nectar homeostasis is reported here for Penstemon. First, nectar removal stimulates replenishment: when nectar was removed hourly for 6 h from P. speciosus, twice as much nectar was secreted cumulatively as when nectar was removed only at the beginning and end of the same 6-h period. Second, replacing artificial nectar in the nectaries of P. speciosus prevents replenishment. Third, the hummingbird-adapted P. barbatus made more nectar before leveling off than the bee-adapted P. strictus. Our work and previous studies with other plants imply mechanisms for dynamic regulation of nectar offerings, at least within broad limits. We speculate about the proximate physiology underlying this behavior and its evolutionary significance.     

A new species of Penstemon (Scrophulariaceae) from Wyoming

A new species from Wyoming,Penstemon gibbensii, is described and contrasted to related species.     

Chromosome numbers in Great Plains species of Penstemon (Scrophulariaceae)

Chromosome numbers are reported for 79 populations ofPenstemon representing 20 species. All but two species counted here are diploids. First counts are reported for seven taxa, all asn=8 or 2n=16.     

A few varietal combinations in Californian Keckiella and Penstemon (Scrophulariaceae)

Combinations are made forKeckiella antirrhinoides var.microphylla, K. rothrockii var.jacintensis, K. ternata var.septentrionalis, Penstemon fruticiformis var.amargosae, P. grinnellii var.scrophularioides, P. heterodoxus var.cephalophorus, P. heterodoxus var.shastensis, andP. newberryi var.berryi.     

An overlooked new species of Penstemon (Scrophulariaceae) from the Great Basin

Penstemon immanifestus, a new species from the Great Basin, is described and illustrated, and its distribution is mapped. Its relationship to other species of subgenus Penstemon, sect. Coerulei, is discussed.     

Vestigial organs as opportunities for functional innovation: the example of the Penstemon staminode

Vestigial organs arise commonly during morphological evolution, but they need not be destined for elimination. Instead, vestigial organs may facilitate functional innovation because their freedom from functional constraints allows them to assume novel roles that their functional progenitor could not perform. We illustrate this vestigial transition between functions with an experimental study of the staminode of Penstemon flowers. Previous phylogenetic and developmental studies indicate that this staminode represents a stamen that was lost phenotypically, but not genetically, and then reappeared in the tribe Cheloneae, to which Penstemon belongs. To assess whether the Penstemon staminode has adopted a novel function(s), we compared pollination of flowers with and without staminodes for two bee-pollinated species, P. ellipticus and P. palmeri, and two hummingbird-pollinated species, P. centranthifolius and P. rostriflorus. The staminode acts differently in the two bee-pollinated species. For P. ellipticus, which represents the basal Penstemon lineage, the staminode hinders pollinator access to nectar, which increases visit duration and pollinator contact with sexual organs, thereby increasing pollen receipt by stigmas and controlling pollen removal from anthers. In contrast, in P. palmeri, the staminode acts as a lever that enhances stigma contact with the pollinator, so that staminode removal reduced pollen receipt, but did not affect pollinator attraction, visit duration, or pollen removal. Unlike in bee-pollinated species. staminode removal from hummingbird-pollinated species did not affect any measured aspect of pollination, indicating that the staminode serves no function in this derived pollination system. These results illustrate several features of vestigial organs: loss of function can be temporary; loss of function facilitates the evolution of novel roles; and functional reinvention will often involve only a single role, thus increasing the chance of both secondary loss of function (bird-pollinated penstemons) and functional switches (P. palmeri).     

Penstemon debilis (Scrophulariaceae): A new species from Colorado endemic to oil shale

Penstemon debilis, collected near Parachute on Mount Callahan in western Colorado, is described and illustrated. The species is endemic to the Parachute Creek Member of the Green River Formation. Oil shale endemism is discussed and the species is compared morphologically to similar species in sectionsGlabri, Coerulei, andPenstemon.     

Assessing hybridization in natural populations of Penstemon (Scrophulariaceae) using hypervariable intersimple sequence repeat (ISSR) bands

Inferences regarding hybridization rely on genetic markers to differentiate parental taxa from one another. Intersimple sequence repeat (ISSR) markers are based on single-primer PCR reactions where the primer sequence is derived from di- and trinucleotide repeats. These markers have successfully been used to assay genetic variability among cultivated plants, but have not yet been tested in natural populations. We used genetic markers generated from eight ISSR primers to examine patterns of hybridization and purported examples of hybrid speciation in Penstemon (Scrophulariaceae) in a hybrid complex involving P. centranthifolius , P. grinnellii , P. spectabilis and P. clevelandii . This hybrid complex has previously been studied using three molecular data sets (allozymes, and restriction-site variation of nuclear rDNA and chloroplast DNA). These studies revealed patterns of introgression involving P. centranthifolius , but were unsuccessful in determining whether gene flow occurs among the other species, and support for hypotheses of diploid hybrid speciation was also lacking. In this study, we were able to fingerprint each DNA accession sampled with one to three ISSR primers and most accessions could be identified with a single primer. We found population- and species-specific markers for each taxon surveyed. Our results: (i) do not support the hybrid origin of P. spectabilis ; (ii) do support the hypothesis that P. clevelandii is a diploid hybrid species derived from P. centranthifolius and P. spectabilis ; and (iii) demonstrate that pollen-mediated gene flow via hummingbird vectors is prevalent in the hybrid complex.     

Ultrastructure of endothelium in ovules of Penstemon gentianoides Poir. (Scrophulariaceae) at mature embryo sac phase

In this study ultrastructural differences between endothelial cells of different location in Penstemon gentianoides have been examined with electron microscope at mature embryo sac phase. Embryo sac is of the Polygonum type and surrounded by endothelium except the micropylar region. The cuticle is located primarily around the chalazal three-fourths of the embryo sac. Endothelium cells around the chalaza and toward the micropylar region are rich in cytoplasmic organelles. The cytoplasm of endothelial cells near the central cell has large vacuoles and few organelles. There are also plasmodesmas on the anticlinal walls of endothelial cells. The endothelium and the micropylar integumentary cells play a role in transport of metabolites into the embryo sac.     

Reproductive assurance varies with flower size in Collinsia parviflora (Scrophulariaceae)

A central question in plant evolutionary ecology is how mixed mating systems are maintained in the face of selection against self-pollination. Recently, attention has focused on the potential reproductive assurance (RA) benefit of selfing: the ability to produce seeds via autonomous selfing when the potential for outcrossing is reduced or absent. To date, there is little experimental support for this benefit under natural pollination conditions. In addition, the RA hypothesis has not been tested experimentally in a species displaying morphological variation for traits expected to influence the mating system, such as flower size, which affects both attractiveness to pollinators and ability to self autonomously. Here, we document significant among-population variation in flower size in Collinsia parviflora and show that pollinators preferred large flowers over small flowers in experimental arrays. The pollinator community varied among three study sites, and two small-flowered populations had lower pollinator visitation rates than one large-flowered population. We compared seed production between intact flowers (can self) and experimentally emasculated flowers (require a pollinator) on large- and small-flowered plants. As predicted by the RA hypothesis, small-flowered plants show a greater RA benefit of selfing than large-flowered plants; emasculated, small flowers produced very few seeds, relative to intact, small flowers or either emasculated or intact, large flowers. We also show that the RA benefit is pollination-context dependent, differing between small- and large-flowered test sites, likely due to a combination of pollinator discrimination against small flowers and differences between test sites in the pollinator community. This paper is the first experimental evidence showing a trait-dependent RA benefit of selfing under natural pollination conditions.     

Two new species of Penstemon (Scrophulariaceae: sect. Saccanthera) from Nevada, U.S.A.

Two Nevada species are described here for the first time: Penstemon tiehmii N. H. Holmgren, which is endemic to Mount Lewis of the Shoshone Range in Lander County; and Penstemon rhizomatosus N. H. Holmgren, which is endemic to the central Schell Creek Range in White Pine County. They both belong to section Saccanthera and are closely related to P. kingii S. Watson, a Great Basin endemic of valley sagebrush habitats. Both new species are talus plants of higher elevations and differ from P. kingii principally in their rhizomatous habit, petiolate leaves, and pubescence of shorter hairs.     

Density and seed set in a self-compatible forb, Penstemon digitalis (Plantaginaceae), with multiple pollinators

Seed production may be limited because flowers do not get enough suitable pollen or because plants lack the resources to make seeds. We used replicated plantings to test factors that influence effects of bumblebee behavior on pollen limitation, as measured by the difference in seed set between hand- and naturally pollinated flowers, of Penstemon digitalis in patches of four to 41 flowering individuals. Seed set per flower was 376% higher in the largest as compared with the smallest Penstemon patches. This positive density dependence reflects activity of long-tongued bees, which (1) have higher effective density as patch size increases, (2) visit greater proportions of plants as patch size increases, and (3) visit smaller proportions of flowers per visited plant as patch size increases. Our results suggest that economics of flight and maneuverability of large, long-tongued bumblebees lead them to transfer more pollen between than within Penstemon plants in large patches. Density of smaller, short-tongued bumblebees was not positively associated with Penstemon seed set, but these bees may be important pollinators at low plant densities. Our experimental system indicates a clear positive relationship between activity of effective pollinators and seed set in a species capable of pollinating itself.     

Nectar yeasts enhance the interaction between Clematis akebioides and its bumblebee pollinator

• It has been hypothesised that intense metabolism of nectar‐inhabiting yeasts (NIY) may change nectar chemistry, including volatile profile, which may affect pollinator foraging behaviours and consequently plant fitness. However, empirical evidence for the plant–microbe–pollinator interactions remains little known.
• To test this hypothesis, we use a bumblebee‐pollinated vine Clematis akebioides endemic to southwest China as an experimental model plant. To quantify the incidence and density of Metschnikowia reukaufii, a cosmopolitan NIY in floral nectar, a combination of yeast cultivation and microscopic cell‐counting method was used. To examine the effects of NIY on plant–pollinator interactions, we used real flowers filled with artificial nectar with or without yeast cells. Then the volatile metabolites produced in the yeast‐inoculated nectar were analysed with coupled gas chromatography and mass spectrometry (GC‐MS).
• On average 79.3% of the C. akebioides flowers harboured M. reukaufii, and cell density of NIY was high to 7.4 × 10⁴ cells mm^?3. In the field population, the presence of NIY in flowers of C. akebioides increased bumblebee (Bombus friseanus) pollinator visitation rate and consequently seed set per flower. A variety of fatty acid derivatives produced by M. reukaufii may be responsible for the above beneficial interactions.
• The volatiles produced by the metabolism of M. reukaufii may serve as an honest signal to attract bumblebee pollinators and indirectly promote the female reproductive fitness of C. akebioides, forming a potentially tripartite plant–microbe–pollinator mutualism.

     

Nuclear ribosomal DNA restriction-site variation in Penstemon section Peltanthera (Scrophulariaceae): an evaluation of diploid hybrid speciation and evidence for introgression

Penstemon spectabilis is a putative stabilized diploid hybrid of P. centranthifolius and P. grinnellii. It is morphologically intermediate, and all three species have different pollinators. Penstemon centranthifolius and P. spectabilis have been proposed as parents of P. clevelandii, which is purportedly isolated by ecological factors. Although hybridization between the proposed parental species has been reported, hybrid swarm formation has not been observed and introgression is purported to be minimal. We tested hypotheses of diploid hybrid speciation and introgression among these species based on rDNA restrictionsite and length variation for 56 populations within and outside of the hybrid complex. Unambiguous molecular markers clearly differentiated P. centranthifolius, P. grinnellii, and P. spectabilis, whereas P. spectabilis and P. clevelandii had the same rDNA type. The P. centranthifolius rDNA type was found in some populations of P. spectabilis and P. clevelandii, but there was no evidence of the additive profile documented for other recent diploid hybrid species. In contrast, the rDNA profile of P. × parishii had a completely additive profile of its proposed parental species P. centranthifolius and P. spectabilis. Ribosomal DNA markers for P. grinnellii were restricted to populations within the species and were not found in any population of P. spectabilis. Our data did not support hybrid-speciation hypotheses, but were in accord with allozyme data that provided evidence for introgression between P. centranthifolius and P. grinnellii, P. spectabilis and P. clevelandii. These results were used to propose criteria to differentiate ancient diploid hybrid speciation from patterns of introgression.