Passiflora represents a diverse group of more than 560 species of vines and trees primarily found in Central and South America. These plants are best known as the source of tropical passionfruit, but are also widely cultivated for their beautiful, complex flowers. Passionflowers appear to be a recently-evolved lineage that has experienced rapid species diversification. Many species are poorly understood with regard to morphology, geographical distribution, and conservation status, especially in the largest lineage of passionflowers, subgenus Decaloba, with 235+ species. This study will synthesize modern and traditional approaches to address these problems, using DNA sequence data, scanning electron microscopy, and observation of fresh and preserved specimens. Field work will enable collection of fresh material and documentation of species distributions. This project will yield a revision of all species in Decaloba, and will provide a modern evolutionary framework within which to address questions about the evolution of floral shape, pollination syndromes, floral development, and the biogeographical history of the lineage.
This study will address important biological and evolutionary questions in an especially charismatic group of plants. Undergraduate and graduate students will participate in the research. Undergraduates at Keene State College and Harris-Stowe State University, institutions that primarily enroll underrepresented groups in the sciences, will especially benefit from involvement in this study. Summer workshops at Rancho Santa Ana Botanic Garden will involve students from the local community. Field expeditions will build international collaborations among U.S. scientists and colleagues in Mexico, Central America, and South America. All results of this project will be available through a website hosted by the Missouri Botanical Garden.
Passion flowers, also known as passion fruit, belong to the genus Passiflora. This genus is primarily known for its exotic flavored fruits, showy flowers, and diverse leaf shapes. More than 550 species are currently described, with the greatest species diversity is found in Mexico, Central and South America. The genus is divided into five groups (subgenera). The largest, subgenus Decaloba, was one of the most poorly understood lineages in the genus. Many new species had been identified, but had not been formally named. The evolutionary relationships among the species were unknown. The relationship of subgenus Decaloba to the rest of the genus was unknown. Interesting cases of pollination were poorly understood and needed further examination. Many rare species needed conservation assessment. While the diversity of this group was apparent, there was no broader context within which to interpret this diversity. Essentially, an evolutionary tree (phylogeny) was needed to provide a framework that would reveal new relationships among these species and provide insights into their history. To address relationships within subgenus Decaloba and begin to understand their evolutionary past, DNA sequences from six genes (three from the nucleus, three from the chloroplast) were used. Approximately 200 species were sampled in total, representing species from Colombia, Brazil, Australia, China, Mexico, the Dominican Republic, and many other countries. Many of these species were collected directly in the field by our team, while others were sampled from herbarium specimens with permission from Missouri Botanical Garden, the Smithsonian, and other botanical research institutions. These data were used to build a well-supported evolutionary tree for subgenus Decaloba. This allowed us to identify the major lineages within the genus: we now know there are eight smaller lineages (supersections) within subgenus Decaloba, each with their own unique characteristics. For example, supersection Xerogona is now much larger than it was before, and it is distinguished by the complete absence of extrafloral nectaries (sugar secreting structures). Nearly all species of Passiflora have these sugar secreting structures, so it is interesting to see an entire lineage distinguished by their absence. With a phylogeny in-hand, several new insights came to light. For example, supersection Disemma, which consists of entirely Asian, Southeast Asian, and Austral-Pacific species, was shown to be one of the most ancient lineages within subgenus Decaloba. Yet its closest relatives are from Central and South America, suggesting a dispersal event from Central/South America to Asia. This lineage is small (ca. 21 species) and species are generally very rare. When compared to the rest of Passiflora, new questions emerge: was Disemma once more diverse in Asia? By what route did they arrive in Asia? Given their rarity, is this lineage on the verge of extinction? The phylogeny yielded further insights into broad evolutionary questions. In Australia, there are three native Passiflora that were hypothesized to be bird pollinated, yet no observations had been made. Bird pollination was suggested because they look nearly identical to several hummingbird pollinated species from Cuba, Dominican Republic, and Jamaica. Yet this similar shape turns out to be a case of evolutionary parallelism, where unrelated species look similar in response to similar evolutionary pressures in their native habitats. The phylogeny showed that the Australian species (supersection Disemma) are only distantly related to those in the Caribbean (supersection Decaloba). Field studies were performed to determine what pollinates the Australian species. Passiflora herbertiana was observed in Queensland. During the study, three avian visitors were observed: the Eastern Spinebill, Lewin's Honeyeater, and the Noisy Miner. These are all species of Honeyeaters, which are the Australian equivalent of hummingbirds in the Caribbean. Thus, viewing these species within the phylogeny revealed a case of parallelism in response to similar pollinator pressures among two distantly related groups of plants. The major goal of this study was to improve our understanding of relationships within subgenus Decaloba, and as such, improve the number of scientific resources available to the public about this group of diverse plant species. General information about subgenus Decaloba is available through Passiflora Research Network website (www.mobot.org/mobot/research/passiflora/). Through field work, we have increased the number of specimens available for study by the scientific community (specimens and images are searchable at Missouri Botanical Garden, www.tropicos.org). New DNA sequences are available for scientists to use in their own analyses via GenBank (www.ncbi.nlm.nih.gov/genbank). Most importantly, this work has and will continue to contribute to improving our understanding of the biodiversity in an economically and ecologically important lineage of plants. With better information about species relationships, conservation assessments will be more accurate and will facilitate the protection of those species that are most vulnerable around the world. As the earth's climate continues to change, and pressures of land use continue to affect species distributions, understanding our biodiversity before it is lost permanently is one of the most important tasks we can hope to accomplish.
