With 700 species of vascular plants, Joshua Tree is renowned for its plant diversity. No wonder that when the area was first proposed for preservation in the early 1930s, the name suggested was Desert Plants National Park. Plant communities, or what we call "associations," describe groupings of various plant species, and are often dependent upon latitude, soil characteristics, and elevation. Using these descriptions makes it easier to understand why certain plants only grow in certain places; it also helps to identify plants in unfamiliar terrain. Plant associations within the park are divided into tree-dominated, shrub- dominated, herbaceous-dominated, and sparse/non-vegetated. Each association is named after the most conspicuous plant in the landscape. Tree-dominated plant associations in the park include: California juniper, singleleaf pinyon, Joshua tree, desert willow, California fan palm, blue palo verde, smoketree, Gooding willow, Freemont cottonwood, and mesquite.
Shrub-dominated associations are the most diverse group, numbering 35. California Mormon tea, creosotebush, creosotebush/white bursage, blackbrush, brittlebush, bigberry manzanita, cheesebush, Mojave yucca, teddy-bear cholla, and desert almond are just a few examples. Herbaceous-dominated associations are those communities that are mostly comprised of species like perennial bunch grasses or annual grasslands. The main associations are big galleta grass and cheatgrass. Sparse/non-vegetated associations include non-vegetated areas (e.g. desert pavement, rock outcrops, dunes, playas, washes, and disturbed areas) and areas with less than two percent shrub cover. These areas may be dominated by annual wildflowers during moist years, but normally appear devoid of vegetation.