Date of Award


Degree Name

MS in Biological Sciences


Biological Sciences


College of Science and Mathematics


Nishanta Rajakaruna

Advisor Department

Biological Sciences

Advisor College

College of Science and Mathematics


San Joaquin wooly-threads (Monolopia congdonii; Asteraceae) is a federally-listed, endangered annual plant species from the desert areas of the San Joaquin Valley. Its limited range puts it at risk of extinction if the climate changes in such a way as to hinder its growth and reproduction. The primary aims of the study were to 1) determine how long-lived the seeds of the M. congdonii are, a key determinant of survival of desert annual plant populations through long droughts and 2) determine how severely hotter, drier conditions impact the ability of emerged plants to grow and reproduce. Secondarily, I aimed to test two hypotheses 1) is seed longevity within the genus Monolopia correlated with habitat aridity? 2) do species’ geographic range limits represent their climatic tolerances? In testing the viability of seeds of Monolopia species collected from herbarium specimens and old field collections, I did not find evidence for the predicted pattern of seed longevity. Though, idiosyncrasies in the data suggest possible issues with the longevity of M. congdonii seeds that are collected prematurely and warrant further investigation to develop best practices for seed collections of this species. To test the climatic tolerance of M. congdonii and the relationship between geographic range and climatic tolerance, I grew several desert annual species under three manipulated water treatments. And while, M. congdonii failed to germinate, the other species showed variable tolerance for the drought treatments but this variability was seemingly unrelated to the species’ geographic range. Importantly, Monolopia lanceolata, a close relative of M. congdonii did not show exceptional vulnerability to the drought-stress conditions relative to other co-occuring species. Taken together, the results of this study enable better informed population viability analyses with the end goal of allowing recovery efforts to succeed.