Key to some common Sonoran Desert plants of SE Arizona

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PDF 6 pages 16 keys 9 species with images by University of Arizona Conservation Biology

Key to some common Sonoran Desert plants of SE Arizona

1. a) Leaves simple. 2
1. b) Leaves compound. 6
2. a) Plant a spiny shrub, branching near the base. Branches long (up to ~2 m) and rarely branching. Stems whitish, longitudinally streaked with green. Stems with stout whitish spines every 3-4 cms along stem. Leaves, when present, in axils of spines. Flowers terminal, red, tubular. Fouqueria splendens, ?Ocotillo?
2. b) Plants not spiny. Shrubs < 2 m tall, more densely branched. Stems brown or green. Leaves variously distributed, but not in axils of spines. Flowers yellow or green, not tubular 3
3. a) Leaves roughly triangular in shape, not deeply lobed. 4
3. b) Leaves oval, or dissected into deep pinnate lobes, not triangular. 5
4. a) Leaves pale grey-green to almost white, leaf margin sometimes undulate or slightly lobed. Pale stems exude a yellow resin where damaged. Flowers borne well above foliage. Flowers yellow, resembling a sunflower. Old flower stalks persistent on nonflowering plants. Encelia farinosa, ?Brittle-bush?
4. b) Leaves pale grey-green to dark grey-green, leaf margins finely toothed. Stems do not exude resin. Flowers borne toward branch tips but not conspicuously above foliage. Flowers green, small, and inconspicuous. Ambrosia deltoidea, ?Triangle-leaf Bursage?
5. a) Plants large shrubs, up to ~1.5 m tall. Leaves oval, leathery, secondary veins obscure. Plants dioecious (different male and female plants). Flowers small, yellow. Seed a large, oily nut. Simmondsia chinensis, ?Jojoba?
5. b) Plants small shrubs or sub-shrubs, usually < .5 m tall. Leaves not leathery, deeply divided into pinnate lobes. Plants monoecious. Flowers yellow, clustered into a composite head (like a thistle flower). Seeds small with cottony pappus. Isocoma tenuisecta ?Burro-weed?
6. a) Leaves opposite, once-compound; leaflets 2 per leaf. Leaves yellowish green and resinous, emitting strong chemical odor when crushed. Fruit a small, white, fuzzy ball. Larrea tridentata ?Creosote Bush?
6. b) Leaves alternate, twice-compound; leaflets more than 2 per leaf. Leaves grayish-green to pale blue-green, not strongly aromatic. Fruit a legume (like a pea pod). 7
7. a) Trunk and stems brown except for the newest growth, not photosynthetic. Leaf divided into 4 sections, each section with >10 pairs of leaflets/leaf section. Propsopis velutina ?Velvet Mesquite?
7. b) Trunk and stems green, photosynthetic. Leaf with only 2 major divisions, each section with fewer than 10 pairs of leaflets/leaf section. 8
8. a) Trunk and stems blue-ish green. Leaflets 4-8 mm long, typically 3 leaflet pairs along rachis. Fruit generally 2-seeded, not strongly constricted between seeds. Cercidium floridum, ?Blue Paloverde?
8. b) Trunk and stems green to yellowish-green. Leaflets 2-3 mm long, typically 4-5 leaflet pairs along rachis. Fruit generally >3-seeded, strongly constricted between seeds. Cercidium microphyllum, ?Foothills Paloverde?

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