For most of the year, the ocotillo (Fouquieria splendens) looks like a spiky, dead stick, but come rain and it leafs out profusely. The ocotillo family consists of 13 species confined to the warm and arid regions of North America.
The ocotillo common to Arizona and Sonora can leaf out completely within 48 hours of a rainfall. If there is no additional rain, the leaves turn yellow and fall off within a few weeks. This cycle can be repeated many times during the year. When the leaf falls off, the petioles (leaf stalks) harden to form spines.
The ocotillo is classified as a woody shrub that can get up to 20 feet high. It flowers in the spring whether or not it has leaves. The bright red to red-orange flowers are pollinated primarily by hummingbirds, but also by insects such as carpenter bees. Ocotillo flowers are frequently the only abundant flower in dry years.
The flowers, when soaked in cold water make a refreshing drink, and the flowers can be used to garnish salads. They usually have a slightly sour taste like lemon. Ocotillo stems are used for house walls, ramada roofs, and fences. Ocotillo stems often take root creating a living fence.
If you look closely at the second photo, you may see that parts of the stem are green. This allows the plant to carry on photosynthesis even when leafless. Ocotillos also have the ability to idle their metabolism to survive long periods of drought.
Ocotillos grow from low elevations up to about 6,000 feet. At higher elevations they prefer to grow on limestone, a fact valuable to geologists. The reason for the limestone preference is that limestone has a higher specific heat than other rocks and thus offers more frost protection to the plant. At hotter, lower elevations, ocotillos grow better in granite because granite weathers into a gravelly soil that retains moisture.
The boojum (Fouquieria columnaris) is a relative of the ocotillo. Boojums are endemic to Baja California and can grow up to 60 feet high. Unlike the ocotillo, the boojum is a succulent. The stem stores water. The stem produces hundreds of non-succulent branches that have spines. Leaves sprout any time moisture is available.
Boojums generally grow in winter and sprout fragrant flowers. The plants can live up to 100 years.
Boojums are pollinated by insects, but it seems that different insect species do the pollination in different years.
According to the Arizona-Sonora Desert Museum, the boojum got its name as follows:
“The English vernacular name comes from Lewis Carroll’s The Hunting of the Snark, a fictitious account of exploration of far-away places. The book contains a mythical creature called the “boojum” which inhabited distant shores. When explorer Godfrey Sykes encountered the plants growing on the desolate Sonoran coast in 1922, he was reminded of Carroll’s story and dubbed them boojums.”
Ocotillo-like plants grow in Madagascar, but these are in a different family, the Didiereaceae. These plants grow much larger and have succulent leaves. That they look like ocotillos is an example of convergent evolution, structure follows environmental conditions.