Cassia eremophila. DESERT CASSIA. Australia
LEGUMINOSAE (Pea family)

Said to represent the finest of Australian wild flowers, desert cassia grows as a small tree in extreme desert conditions where avoidance of evaporation has reduced the leaves to needles. Consequently, the abundant bright yellow bell flowers, which endure for quite some time, present a spectacular show. Seed pods, resembling those of acacias, contain hard shiny seeds. This small tree believes that the summer will kill it, so it providentially supplies fresh shoots from its base. Even though the top is not killed here in the Bay Area, you might as well prune to favor the new shoots. The tree produces volunteer seedlings at 836 Santa Fe Avenue, but has not reached tree size here. Cassia artemisioides may also occur in private gardens.

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The Pea family is among the largest flowering plant families with about 18,000 species in 630 genera worldwide. Caesalpina is the type genus for the Fabaceae subfamily Caesalpinioideae, following Cronquist (1981). This subfamily is intermediate in flower morphology between the other two higher-level classifications Mimosoideae and Faboideae (or Papilionoideae). The latter and largest group includes plants with papilionaceous, "butterfly-like", corollas (with standard, wings, and keel)—as the common garden pea.

All subfamilies are well represented on campus for closer study. Caesalpinioideae and Mimosoideae include mainly tropical trees with pinnately or bipinnately compound, alternate leaves. Mimosoideae flowers are regular (radially symmetrical), the corolla with equal petals often fused into a tube. Campus representatives include Acacia, Albizia, and Gymnocladus. Caesalpinioideae flowers are usually more or less zygomorphic (divisible into equal halves in one plane only). As with Caesalpina spp., the petals are distinct, the uppermost often smaller than the laterals. Other campus members of the subfamily include Bauhinia, Cassia, Cercis, Gleditsia, and Parkinsonia. It would be instructive to work out the higher classification of the many other campus peas (genera listed in the family index) from field observation throughout the year.

— further reading: Wendy Zomlefer, Guide to Flowering Plant Families, Univ. of North Carolina Press, 1994.

Name derivation, genus | species Greek name for a species of leguminous plants providing the senna leaves and pods important to pharmacy | Greek eremia (desert) and philos (friend), i.e., desert-lover

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