This list isn't intended to make you comfortable reading botanist-targeted plant-identification books, most of which are copied directly from eye charts, but simply to introduce you to the limited selection of technical terms used in the Yosemite Wildflower Guide. If you'd like a more complete roundup of botanical jargon, try the guides at CalFlora and Dave's Garden, which can provide useful insight in the event you find a group of botanists glancing your way and muttering words like 'glabrous' or 'vermicular'. If you seek a diagram identifying the various flower bits, here's one at Wikipedia (though it somehow overlooks the pistil).
Annual: Plants that live and die in a single season; the mayflies of the plant world. Other categories include biennial (living two years, flowering one) and perennial (living and flowering three or more years).
Biennial: Plants that live two years and flower during their second season. Other categories include annual (living one year) and perennial (living and flowering for three or more years).
Bracts: Specialized leaves that grow near the flower, often appearing more like petals than conventional leaves. On Mountain Dogwood, for instance, what appear to be large white petals are actually bracts. Bracts typically serve to protect the flower or attract pollinators.
Endemic: Plants that are native to a particular area (usually California, in our case) and grow nowhere else in the known universe. For comparison, see native and invasive.
Invasive: Plants that have arrived in Yosemite via unnatural means, usually human-aided at some point. For comparison, see native and endemic.
Lanceolate: Slim and tapering towards a point at one end, like an arrowhead. See Tincture Plant leaves for an example.
Native: Plants that arrived in Yosemite through natural means, via evolution or distribution by wind, animals, etc., and also grow in regions other than Yosemite. For comparison, see endemic and invasive.
Perennial: Plants that can survive and flower for three or more years. Other categories include annual (living and flowering for one year or less) and biennial (living for two years, flowering during the second year).
Sepals: Specialized leaves that enclose and protect the flower during the bud stage. You can see the sepals on both a bud and a blooming flower (the sepals are white with green stripes on the opened flower) on this Globe Lily photo. On some plants, such as Western Rue Anemone, that don't have petals, what appear to be petals on the opened flower are actually the sepals.
Umbrel: A flower cluster sprouting from the central stem in a semi-spherical shape, like an inside-out umbrella. See Pretty Face flower clusters for a typical example.