Gary Hannan

A photo of Gary Hannan


Biology; Environmental Science and Society (ENVI) Interdisciplinary Program

401H Science Complex


[email protected]


  • BA, University of California, Santa Barbara, 1973
  • Ph.D., University of California, Berkeley, 1979

Interests and Expertise

My research focuses primarily in the reproductive biology of plants (pollination biology, mating systems, clonal reproduction) and on the effects of reproductive biology on genetic diversity and population processes. One project has included studies of the reproductive biology and genetic diversity in the threatened species Iris lacustris (Dwarf Lake Iris) and its sister species Iris cristata (Dwarf Crested Iris). Students and I have found that I. lacustris has very little genetic diversity, whereas the widespread I. cristata is highly variable. Both species have similar reproductive systems, so explanations of low genetic diversity in I. lacustris rely on historical effects (evolutionary and biogeographic processes). Another project concerned changes in male vs female reproductive allocation in flowers of an annual poppy (Platystemon californicus) at different developmental stages of the plants in response to environmental factors. Patterns of allocation of resources to sexual vs. asexual reproduction and growth in Starflower (Trientalis borealis) is a more recent project. Previous studies have included comparative pollination biology of co-occurring taxa of Caulophyllum (Berberidaceae) and responses of Valeriana ciliata to early spring burning. I continue to provide taxonomic treatments of the genus Eriodictyon (Yerba Santa) and the poppy family (Papaveraceae) for the Flora of North America and The Jepson Manual: Higher Plants of California.


  • BIO 120 Introductory Biology II
  • BIO 130 Biology of Plants
  • BIO 412 Biogeography
  • BIO 455 Plant Evolution and Classification
  • BIO 458 Trees and Shrubs
  • BIO460 Plant Anatomy
  • BIO 412G Biogeography (Graduate)
  • BIO 555 Plant Evolution and Classification
  • BIO 558 Trees and Shrubs
  • BIO 460G Plant Anatomy (Graduate)

Publications and Presentations

  • Hannan, G.L. Taxonomic treatment of Papaveraceae. The Jepson Manual: Higher Plants of California. University of California Press (submitted 2008).
  • Hannan,G.L. 2008. Treatment of Hydrophyllaceae for Nuevo Catalogo de la Flora de Venezuela. Omaira Hokche, ed. Fundacion Instituto Botanico de Venezuela (nomenclatural research and clarification of current nomenclature).
  • Hannan, G.L. Taxonomic treatments of Hesperomecon, Meconella and Platystemon (Papaveraceae). The Jepson Manual: Higher Plants of California. University of California Press (submitted 2006).
  • Hannan, G.L. Taxonomic treatment of Eriodictyon (Hydrophyllaceae). The Jepson Manual: Higher Plants of California. University of California Press (submitted 2006).
  • Hannan, G. L. 2005. Effects of controlled burns on vegetative growth and sexual reproduction in Valeriana ciliata in a Michigan fen. Michigan Botanist 44: 149–157.
  • Hannan, G. L. and M. Orick. 2000. Isozyme diversity in Iris cristata and the threatened glacial endemic Iris lacustris (Iridaceae). American Journal of Botany 87: 293–301.
  • Hannan, G. L. and Prucher, H. 1996. Reproductive biology of Caulophyllum thalictroides (Berberidaceae), an early flowering perennial of eastern North America. American Midland Naturalist 136:267–277.