Phylogeny, Character Evolution, and Biogeography of Sisyrinchium (Iridaceae)

Lisa Karst, Ph.D., Rancho Santa Ana Botanic Garden, c.v.

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My project is primarily a phylogenetic investigation of Sisyrinchium (Iridaceae), a New World genus of approximately 140 species, though there are over 400 names in the genus. I have identified morphological characters supporting the groups resolved by Bayesian analyses of nuclear and chloroplast DNA markers. I have also examined biogeographic patterns revealed by these analyses. The loss of specialized pollinator relationships that are found in species at the putative area of origin, Argentina, has been proposed as key in the radiation of section Sisyrinchium (the blue-eyed grasses) across South America and into North America. Concerted morphological and pollinator shifts leading to radiations across broad geographic regions deserve greater investigation. Preliminary data indicates that specialized pollinators may have been both gained and lost in Sisyrinchium. This project also compares the relative importance of the Antillean corridor and the Mesoamerican land bridge in plant dispersal to North America.

Greater species diversity of Sisyrinchium in central South America suggests that it originated there, and this genus has a north to south pattern of distribution along coastlines, mountain chains, and inland prairies that might have acted as corridors of speciation. Series of mountain endemics may have originated from adjacent lowland species, or may be isolates of a widespread tropical species of the ice ages. The combination of endemism and rapid radiation is an important evolutionary phenomenon usually reported for isolated island areas such as Hawaii and the Galapagos.

This genus is economically and culturally important in that several species are cultivated as ornamentals, one species is a weed that causes significant illness to South American cattle, one is used in Peru as a topical treatment, and another species is part of the Hawaiian religious traditions. Twelve of the thirty-seven species recognized in the Flora USA are listed (NatureServe Explorer, 2006) as at risk (G3 or worse) over some part of their range. These species are S. acre, S. arizonicum, S. dichotomum, S. farwellii, S. funereum, S. hitchcockii, S. longipes, S. pallidum, S. radicatum, S. sarmentosum, S. septentrionale, and S. xerophyllum.

• Goals and Objectives
• Results and Conclusions
• Future Directions
• Bibliography

Goals/Objectives:

1. The current circumscription of two subgenera does not adequately represent the diversity within Sisyrinchium.
2. Evolution of key floral characters has provided opportunity for this genus to shift pollinators and radiate, as hypothesized by Drs. Cocucci and Vogel (2002).
3. The ancestor of section Sisyrinchium occurred in South America. There were two radiations of blue-eyed grass into North America.

Results and Conclusions:

Molecular, morphological and anatomical characters support eight sectional divisions and show subgenus Ecthronema to be a basal grade rather than a clade. Yellow forms with a single rhipidium subtended by multiple bracts partially fused filament columns and spreading style arms are basal. These species are confined to the tropical Andes. Blue-eyed grasses (subgenus Sisyrinchium) are not monophyletic either, but comprise at least two separate clades. Intervening between these two clades is a group of anomalous species usually treated as members of the yellow-eyed grasses (subgenus Ecthronema), but thought by some researchers to be of hybrid origin between the subgenera, based on strong karyotype and anatomical data.

Based on center of diversity, MacClade character reconstruction, Bremer's ancestral area, and DIVA analysis, genus appears to have originated in the cental Argentina, though several sections diversified elsewhere. Several of the sections are widespread across the Americas (sections Sisyrinchium, Mesmeria, and Sipacapa), while other sections are geographically restricted. Section Spathirachis is restricted to the range of the specialized pollinator, which is derived within the section. No evolution away from specialized pollination within this group has been observed. Multiple dispersals within section Sisyrinchium into North America seem to have followed the Sierras, the coastlines, and the central plains. Two radiations occurred, one through central Mexico, and one possibly via the Antilles, lacking any Mexican elements.

Endemic species of both North and South America are sister to sympatric or parapatric common taxa rather than to each other.

Future Directions:

There is no modern monograph of Sisyrinchium, and until now, there has been no broad molecular study of the genus. Almost every worker who has addressed the Sisyrinchium in the last generation has noted that the group is in a state of near total disarray. My project breaks this tangle into workable pieces, so that this large and confused genus can be resolved.

Sisyrinchium minus, having only 5 very small chromosomes, has the smallest known genome in the Iridaceae and likely in the Asparagales. It is comparable to that of other monocots whose genomes have been fully sequenced (such as corn, wheat, barley and rice) (NCBI Genomes, 2006). Within the Asparagales, there is a lack of information on genomic structure, despite the many valuable crop and ornamental plants within this group: Asparagus, Allium (onion, garlic), Iris, Gladiolus, Crocus (saffron), Orchid (vanilla), Aloe, Agave, Amaryllis, Agapanthus, Gallianthus, and Daffodil. Working with Sisyrinchium positions me to be involved in exciting work on basic concepts in evolution and development.