Systematics Section / ASPT
Park, Michael S. .
Evolution of seasonal heterophylly in vernal pool Eryngium (Apiaceae).
SEASONAL heterophylly in the vernal pool Eryngium (Apiaceae) of California appears to be an adaptation to the harsh annual fluctuations in water availability. Vernal pools are inundated through the wet season, and often thoroughly desiccated by mid-summer. Winter leaves are tubular, hollow and septate -- a feature shared by many wetland plants such as Juncus (Juncaceae), and may serve as a conduit for oxygen to the meristematic tissue at the base. These winter leaves are identical to the leaves produced by juvenile plants and seem heteroblastic. By summer, these are succeeded by leaves with well developed laminae. If sufficient water is present in the soil during summer drought, then the root caudex may survive to sprout fresh juvenile leaves the following winter. Leaf morphology appears to be primarily under the control of photoperiod, but inundation by water may also be an influence. This feature continues to exist in E. jepsonii whose habitat is strictly terrestrial. This is attributed to trait conservatism and habitat shift.Seasonally heterophylly is also reported from Eryngium vesiculosum found in eastern Australia and New Zealand. Herbarium specimens of E. sparganoides in Chile are strongly suggestive of heterophylly, but those of E. cervantesii in Mexico are less certain. Fieldwork and common garden studies should augment these observations. This trait may be an exaptation for vernal pool conditions and may have originated in seasonally wet habitats such as meadows, lake shores, and stream banks. Phylogenetic studies are in progress to test this possibility. They may also show whether this trait has evolved independently in different lineages or is a synapomorphy for a larger group adapted for seasonally inundation. The results of preliminary phylogenetic work are to be presented.
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1 - University of California, Berkeley, Department of Integrative Biology, University and Jepson Herbaria, 1001 Valley Life Sciences Bldg. #2465, Berkeley, California, 94720, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Wednesday, August 2nd, 2006
Time: 1:00 PM