Systematics of California Grasses (Poaceae)

The grass family (Poaceae or Gramineae) is the fourth largest flowering plant family in the world and contains about 11,000 species in 800 genera worldwide. Twenty-three genera contain 100 or more species or about half of all grass species, and almost half of the 800 genera are monotypic or diatypic, i.e., with only one or two species (Watson and Dallwitz 1992, 1999). Over the last 150 years the grass flora of California has been the subject of considerable attention by botanists. Bolander (1866) prepared the first comprehensive list, recognizing 112 grasses from California, of which 31 were introductions. Thurber (1880) mentions 175 grasses in California, and Beetle (1947) enumerates 400 known species. It is interesting to note that Crampton (1974) recognized 478 grasses in California, and of these, 175 were introduced and 156 were reported as annuals (we report 152 annuals here). We recognize 524 grass species in 144 genera; of these, 233 (44.5%) species in 65 genera are introduced (see Appendix 1), and the remaining 291 (55.5%) species in 79 genera are native. Thirty-seven species are endemic to California. One hundred fifty-two grasses in California are annual; of these 101 are introduced and 51 are native. Obviously the grass flora has been altered by humans, especially over the last 300 years since European settlement. The percentage of introduced grasses is perhaps higher in California than in any other state, simply because there are many different habitats (from 212 feet below sea level in Death Valley to 14,496 feet on top of Mount Whitney) available for colonization of weedy species. In addition, many annual species and genera of Mediterranean origins have found suitable habitats in California (see D'Antonio et al.. Chapter 6). To understand the important adaptations within the grasses, a firm grasp of the unique morphological features that define this family is needed. We start this chapter with an introduction to the morphology and ecology of grasses and then discuss the phylogeny (evolutionary relationships among organisms) of the major tribes of California grasses.