Monsoons are Here!

July 11, 2010

Hot, humid, and hazy, with spectacular cloud buildups and (if we’re lucky that day), RAIN.  It’s been humid for a couple of weeks, but the first rain only arrived last night, washing the dust off the trees and giving the seeds of monsoon wildflowers a wake-up call, though we won’t see them for awhile yet.  In the encinal, the grassy evergreen oak woodlands on the lower slopes of southeastern Arizona mountains, one wildflower arrives early, as a harbinger of the monsoons:  Jatropha macrorhiza appears as the clouds gather, and the first blooms open before the rains begin.  This plant has no good common name.  It is a perennial herb that sprouts from a huge brown potato-like tuber.  The tuber stores winter rain like a cask, and replenishes its store during the monsoons, after flowering.  It is common in a narrow elevation range in southeastern Arizona, but found in only a few localities in Texas and New Mexico, perhaps because it is so dependent on Arizona’s unique biseasonal rainfall pattern.  The plant is in the Euphorbiaceae or Spurge Family, which isn’t obvious until you look at the seedpods.  Southern Arizona’s other Jatropha species, J. cardiophylla, is a small woody shrub with heart-shaped leaves that is mostly confined to lower elevations in the Sonoran Desert, thought the two plants may occasionally grow side by side in the Empire, Rincon, and Santa Rita Mountains.  I took this photo today in the Sierrita Mountains:

Jatropha macrorhiza

Another photo from the Sierritas, a small mountain range almost entirely covered in oak woodland.  I took this one last weekend.  It is Arizona black oak or bellota, Quercus emoryi, with a blooming Agave parryi flowerstalk.  You can see a bluish-gray agave leaf rosette (not the one that is blooming) near the bottom of the photo.  The “grass” at the bottom of the picture is Nolina microcarpa (called sacahuista, beargrass, or nolina), which is not a grass at all, but a relative of Agave and Yucca.

Agave and Oak in the Sierrita Mts.


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