Erin A. Tripp

IS FLORAL SPECIALIZATION AN EVOLUTIONARY DEAD‐END? POLLINATION SYSTEM TRANSITIONS IN RUELLIA (ACANTHACEAE)

Abstract “…the highly developed, or specialized types of one geologic period have not been the parents of the types of succeeding periods, but …the descent has been derived from the less specialized of preceding ages…” —Edward D. Cope (1896), pp. 173–174 Pollination systems frequently reflect adaptations to particular groups of pollinators. Such systems are indicative of evolutionary specialization and have been important in angiosperm diversification. We studied the evolution of pollination systems in the large genus Ruellia. Phylogenetic analyses, morphological ordinations, ancestral state reconstructions, and a character mapping simulation were conducted to reveal key patterns in the direction and lability of floral characters associated with pollination. We found significant floral morphological differences among species that were generally associated with different groups of floral visitors. Floral evolution has been highly labile and also directional. Some specialized systems such as hawkmoth or bat pollination are likely evolutionary dead-ends. In contrast, specialized pollination by hummingbirds is clearly not a dead-end. We found evidence for multiple reverse transitions from presumed ancestral hummingbird pollination to more derived bee or insect pollination. These repeated origins of insect pollination from hummingbird-pollinated ancestors have not evolved without historical baggage. Flowers of insect-pollinated species derived from hummingbird-pollinated ancestors are morphologically more similar to hummingbird flowers than they are to other more distantly related insect-pollinated flowers. Finally, some pollinator switches were concomitant with changes in floral morphology that are associated with those pollinators. These observations are consistent with the hypothesis that some transitions have been adaptive in the evolution of Ruellia.

Evolutionary Relationships Within the Species-Rich Genus Ruellia (Acanthaceae)

Abstract Phylogenetic relationships among species of the large genus Ruellia (Acanthaceae) have never been studied. Ruellia, with approximately 300 species, is geographically widespread and morphologically diverse. Molecular data for 196 specimens from the nuclear ribosomal ITS region and the chloroplast trnG-trnR region were used to test monophyly of the genus against closely related genera in Ruellieae, to reconstruct phylogenetic relationships among species of Ruellia on a global scale, to re-evaluate previous morphology-based classifications, and to examine the utility of morphological characters, especially corolla morphology, for future sectional delimitation. Bayesian and parsimony analyses indicate four genera are evolutionarily allied to Ruellia. Acanthopale is sister to Ruellia s. l. with strong support. Blechum, Eusiphon, and Polylychnis are nested within Ruellia s. l., and species in Eusiphon and Polylychnis are here formally transferred to Ruellia resulting in the new combinations Ruellia geayi and Ruellia fulgens. Ruellia s. l., including Blechum, Eusiphon, and Polylychnis, is monophyletic but only weakly supported by parsimony. Within Ruellia, Old World taxa form a basal grade and New World taxa are monophyletic and nested within the Old World grade. Alternative hypotheses involving non-monophyly of New World Ruellia were significantly less parsimonious and less likely. Within New World Ruellia, many clades are informally recognized, several of which reflect previous taxonomic groupings to some extent. Constraining all putatively hummingbird-pollinated taxa to monophyly was strongly rejected. This suggests that corolla morphology has undergone convergent evolution and is therefore likely an inappropriate character for sectional delimitation, contrary to previous use.

A rich fossil record yields calibrated phylogeny for Acanthaceae (Lamiales) and evidence for marked biases in timing and directionality of intercontinental disjunctions.

More than a decade of phylogenetic research has yielded a well-sampled, strongly supported hypothesis of relationships within the large ( > 4000 species) plant family Acanthaceae. This hypothesis points to intriguing biogeographic patterns and asymmetries in sister clade diversity but, absent a time-calibrated estimate for this evolutionary history, these patterns have remained unexplored. Here, we reconstruct divergence times within Acanthaceae using fossils as calibration points and experimenting with both fossil selection and effects of invoking a maximum age prior related to the origin of Eudicots. Contrary to earlier reports of a paucity of fossils of Lamiales (an order of ∼ 23,000 species that includes Acanthaceae) and to the expectation that a largely herbaceous to soft-wooded and tropical lineage would have few fossils, we recovered 51 reports of fossil Acanthaceae. Rigorous evaluation of these for accurate identification, quality of age assessment and utility in dating yielded eight fossils judged to merit inclusion in analyses. With nearly 10 kb of DNA sequence data, we used two sets of fossils as constraints to reconstruct divergence times. We demonstrate differences in age estimates depending on fossil selection and that enforcement of maximum age priors substantially alters estimated clade ages, especially in analyses that utilize a smaller rather than larger set of fossils. Our results suggest that long-distance dispersal events explain present-day distributions better than do Gondwanan or northern land bridge hypotheses. This biogeographical conclusion is for the most part robust to alternative calibration schemes. Our data support a minimum of 13 Old World (OW) to New World (NW) dispersal events but, intriguingly, only one in the reverse direction. Eleven of these 13 were among Acanthaceae s.s., which comprises > 90% of species diversity in the family. Remarkably, if minimum age estimates approximate true history, these 11 events occurred within the last ∼ 20 myr even though Acanthaceae s.s is over 3 times as old. A simulation study confirmed that these dispersal events were significantly skewed toward the present and not simply a chance occurrence. Finally, we review reports of fossils that have been assigned to Acanthaceae that are substantially older than the lower Cretaceous estimate for Angiosperms as a whole (i.e., the general consensus that has resulted from several recent dating and fossil-based studies in plants). This is the first study to reconstruct divergence times among clades of Acanthaceae and sets the stage for comparative evolutionary research in this and related families that have until now been thought to have extremely poor fossil resources.

Phylogenetic relationships within Ruellieae (Acanthaceae) and a revised classification.

Phylogenetic knowledge of the large plant family Acanthaceae has been greatly advanced over the last 2 decades. Studies have demonstrated the existence of several major lineages, most of which have been the focus of subsequent investigation. Missing among these is comprehensive study of the 48 genera currently classified in tribe Ruellieae, a pantropical lineage that includes several species-rich genera. We compared the number of validly published names to current estimates of species richness per genus in Ruellieae and found more than 2600 names available for ∼1200 species. Using molecular data from two nuclear (ITS+5.8S, Eif3E) and three chloroplast (trnG-trnR, trnG-trnS, psbA-trnH) markers, we test the placement of these 48 genera in Ruellieae, explore the monophyly of currently recognized taxa, and propose morphological features to diagnose major clades within the tribe. We were able to sample all but four of 48 genera, and all were resolved in Ruellieae except Zygoruellia. Many monospecific or oligospecific genera are nested within clades of more species-rich genera. We propose several new generic synonymies to reflect these results and insights from morphology. Finally, we present a revised classification of Ruellieae that contains seven subtribes. A solid phylogenetic hypothesis of relationships within Ruellieae contributes to progress in biology in three important ways: (1) it enables better assessment of trait homologies and thus characters upon which genera are delimited, (2) it contributes to the Global Strategy for Plant Conservation’s initiative to document plant biodiversity, and (3) it facilitates cross-family comparative evolutionary analyses, including large-scale hypothesis testing of biogeographic patterns, clade size asymmetries, and differential diversification within Acanthaceae.

Resolving the genus Graphina Müll. Arg. in North America: new species, new combinations, and treatments for Acanthothecis, Carbacanthographis, and Diorygma

As part of our ongoing studies of the Graphidaceae in North America, we resolve the status of all taxa traditionally assigned to the genus Graphina that have been reported from the continent north of Mexico. Treatments for the North American members of Acanthothecis, Carbacanthographis, and Diorygma are presented because several species of Graphina have been reassigned to these genera, and our studies of accumulated herbarium materials revealed the existence of several previously unreported and unrecognized species. The following new combinations are made: Acanthothecis leucopepla, A. mosquitensis, A. peplophora, and A. poitaeoides. Carbacanthographis muriformis is described as new to science based on material from Florida. The following taxa are reported from North America for the first time: Acanthothecis poitaeoides, Diorygma junghuhnii, D. reniforme.

Taxonomic Revision of Ruellia Section Chiropterophila (Acanthaceae): a Lineage of Rare and Endemic Species from Mexico

Abstract Ruellia section Chiropterophila as here recognized contains 11 species endemic to areas in and around the transnational Volcanic Belt of México: the Sierra Madre del Sur, the Balsas Depression, and the Altiplano. Most of these species are rare, and nearly half are known only from one or two collections. Of the remaining six, two are restricted to single states. One species described as new to science, Ruellia laslobasensis , is distinguished from a close relative by its smaller corollas, calyces, and fruits. Ruellia chilpancingana is placed into synonymy with R. sororia. Ruellia section Urceolata is synonymized with sect. Chiropterophila. Two species previously treated in sect. Chiropterophila, Ruellia petiolaris (as R. palmeri) and R. carmenaemiliae, are excluded from the section. Phylogenetic analyses using three chloroplast markers (trnC-trnR, trnG-trnS, psbA-trnH) and one nuclear marker (ITS + 5.8S) were conducted to test the monophyly of sect. Chiropterophila and to reconstruct relationships among species. Sequences were successfully generated for all species in sect. Chiropterophila; some are known only from old herbarium material. One of these, collected in 1894, is among the oldest known plant herbarium specimens to be successfully sequenced. Analyses reveal that section Chiropterophila is monophyletic but not well supported; an alternative hypothesis of nonmonophyly of the section could not be rejected. Species descriptions, botanical illustrations, and a dichotomous key to distinguish the 11 taxa in Ruellia sect. Chiropterophila are provided.

Contributions to The Lichen Flora of North Carolina: A Preliminary Checklist of the Lichens of Gorges State Park

Abstract Here we present a preliminary checklist of the lichens of Gorges State Park, North Carolina, and describe Gyalectidium appendiculatum, a foliicolous lichen species new to science. Gorges State Park and the surrounding region encompasses a series of north- to south-facing drainages characterized by steep slopes and abrupt elevational changes, high levels of rainfall, and year-round moderate temperatures. The gorges harbor several rare and endemic taxa. This survey represents the first attempt to describe the lichen diversity of this region. We collected 441 specimens that yielded a total of 218 species. Using Jaccard indices, we calculated species composition similarities between Gorges State Park and three additional sites in North Carolina (two other mountain checklists and one coastal plain). Comparisons among the three mountain sites resulted in the highest similarity indices. However, Gorges State Park had more affinities to the coastal plain flora than did either of the other two mountain sites. These data contribute new information about eastern North American lichens as well as add to the growing documentation of the extraordinary and unique biological composition of the western North Carolina gorges. Future research on the lichen flora of Gorges State Park will undoubtedly lead to new discoveries.

Buellia Japonica (Physciaceae), a New Lichen Record for North America

Abstract The lichen Buellia japonica is reported for the first time from North America based on collections from Gorges State Park, North Carolina. A description of the species is provided and its generic placement is discussed.

Natural history, distribution, phylogenetic relationships, and conservation of Central American black walnuts (Juglans sect. Rhysocaryon)1

Abstract The tree genus Juglans (nogal, walnut) is generally thought of as a north temperate group, but most of the 16 species of black walnuts (Juglans sect. Rhysocaryon) occur in subtropical areas of the New World, spanning Central America, Andean South America, and the Greater Antilles. The two species native to Central America (J. olanchana var. olanchana and J. steyermarkii) and two closely related Mexican taxa (J. olanchana var. standleyi and J. pyriformis) have not been studied thoroughly from a comparative systematic perspective, so here we provide a detailed investigation of their morphology and natural history as a first step towards a broad-based synthesis of J. sect. Rhysocaryon. Fieldwork in Guatemala and Mexico provided the material for germination studies, morphological analyses, and phylogenetic reconstruction using DNA sequences. Juglans steyermarkii was rediscovered in its type locality in Guatemala, and new populations were located during the course of fieldwork. SEM analysis of trichome diversity and density, along with leaflet shape, provided characters to differentiate among five taxa of Juglans in the accompanying key. Staminate flowers and pollen examined for the first time in J. steyermarkii showed close morphological similarities to those of other species of black walnuts. Variation in the pattern of nut-wall sculpture appears to be a promising source of variation; however, adequate capture and quantification of this variation will likely require three-dimensional scanning techniques. There was high variability in percent seed germination of the two Central American species and no observed advantage to leaching, scarification, or a prolonged stratification period. DNA studies included in the exploration of three promising sources of nuclear sequence variation: the ETS and ITS (external and internal transcribed spacer of ribosomal DNA), and the second intron of the LEAFY gene. Combined phylogenetic analysis of these sequences provided a moderately resolved topology containing two major groups of black walnuts and a general correlation between phylogeny and geography. The analyses supported a division between taxa from northern Mexico and the USA, and those from southern Mexico, Guatemala, the West Indies (Greater Antilles), and South America. Observations on the geographic range of Juglans in Mexico and Guatemala indicated a frequent association with coffee plantations, suggesting similar climatic requirements. Our studies of the dispersed and most likely fragmented populations indicate that Juglans may still be found in native plant communities as a canopy tree, although it is much more common to observe populations in cleared areas where the trees were retained as shade for coffee. We are not aware of any major efforts to conserve the native nogal in Central America, though they are sometimes left and/or planted as shade trees in coffee fincas. A study conducted in Mexico suggests that Juglans might be useful in agroforestry efforts to rehabilitate degraded sites.

Origin of African Physacanthus (Acanthaceae) via wide hybridization.

Gene flow between closely related species is a frequent phenomenon that is known to play important roles in organismal evolution. Less clear, however, is the importance of hybridization between distant relatives. We present molecular and morphological evidence that support origin of the plant genus Physacanthus via “wide hybridization” between members of two distantly related lineages in the large family Acanthaceae. These two lineages are well characterized by very different morphologies yet, remarkably, Physacanthus shares features of both. Chloroplast sequences from six loci indicate that all three species of Physacanthus contain haplotypes from both lineages, suggesting that heteroplasmy likely predated speciation in the genus. Although heteroplasmy is thought to be unstable and thus transient, multiple haplotypes have been maintained through time in Physacanthus. The most likely scenario to explain these data is that Physacanthus originated via an ancient hybridization event that involved phylogenetically distant parents. This wide hybridization has resulted in the establishment of an independently evolving clade of flowering plants.