Saturday, July 1, 2017

California Spring Extravaganza 4. Cacti and cactus wannabees

Natural cactus gardens are common in the rocky slopes of Anza-Borrego.
No plants are more symbolic of deserts than cacti, and so they deserve a post of their own.  The cactus family consists of some 1750 species, almost exclusively inhabitants of the new world, and amply represented in the California desert.  So successful is the leafless, succulent habit of these plants, that regions of the world where the cactus family has not spread, have evolved their own cactus look-a-likes, or "wannabees" (want-to-be's) in the American slang.  In Africa, both the Euphorbiaceae and the Asclepiadaceae have produced their own cactus-like plants in great variety (see South Africa.8. Succulent Paradise, and others in the series).  And then there are the leaf succulents, Kalanchoe plus Aloe and their relatives in Africa, Agave, Sedum, in the new world.

The Ocotillo bush, Fouquieria splendens,
 superficially resembles a cactus.
In Anza-Borrego, a spectacular cactus mimic, ocotillo, is abundant. One can tell it is not a true cactus because after the rainy season its succulent stems are studded with small leaves, and the flowers are very different.  In the dry season, the leafless succulent stems could easily be mistaken for a thin-stemmed cactus.
In the rainy season, ocotillo sprouts small leaves.
Ocotillo flowers are produced in long racemes at the ends of the stems.

Ocotillo flowers are narrow-tubular, and pollinated by migrating hummingbirds that feed on their nectar.

The common beaver tail cactus in Anza-Borrego is
Opuntia basilaris.  A possible adaptive advantage
of the flattened stem segments is that the
noon-day sun strikes the surface obliquely.  This
may reduce the risk of overheating.
Like all cacti, the flowers of beaver tail cacti have
numerous petals and stamens.
Now for the real cacti.  Members of this family are leafless, except for some archaiec genera like Pereskia.  Actually, what were originally leaves in cactus ancestors were modified into spines, which occur in concentrated clusters along the stem,  Flowers in this family are large, with many petals and stamens, and an inferior (i.e. located below the petals and stamens) ovary with numerous seeds. So in flower, they are even more easily distinguished from their imitators. In Anza-Borrego several common growth forms are represented, including barrel cacti, cylindrical cacti, and beavertail cacti (having flattened, oval-shaped stem segments).

Mammillaria dioica is a small barrel cactus, and its stem is shaded by numerous long spines.

Cylindropuntia echinocarpa is one of the cylindrical cacti known as cholla.

Ferrocactus cylindraceus is another barrel cactus, here bedecked by a ring of flowers.
The flowers of Echinocereus engelmannii, a hedgehog cactus, resemble the beaver tail cactus that inhabits the same rocky slopes, but its stems are cylindrical. Photo by Gretchen Craig.

In this photo, the green stigmas of Echinocereus are seen in the center of the flower. Photo by Gretchen Craig.

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