Plant Species of the Borrego Desert: Nyctaginaceae: Boerhavia species, spiderlings

A. "Spiderling" dead stems from the previous year, resembling a spider's web, with new growth from the current year at left, seen on 22 February 2011 in the wash immediately south of Glorietta Canyon. (pix with scale) B. Greatly-Magnified Inflorescence from Harper Canyon, 19 January 2011 (pix with scale from 18 March 2011)

Fig. 1. Pictures of Boerhavia coccinea.

Boerhavia is a genus of about 40 species found worldwide in warm-temperate and tropical regions. Four species are native to California, all of which are found in Anza-Borrego Desert State Park.

The genus was named for H. Boerhaave, a Dutch botanist who lived from 1668 to 1738, by Linneaus, who intentionally Latinized the name, getting rid of the double "a".

Wikipedia states that the common name for the genus of spiderling refers to the appearance of a spider or spider's web given by the numerous long, slender and interlocking stems of the inflorescences. In the Borrego Desert, only our single perennial species, B. coccinea, resembles a spider's web from its numerous branches spread along the ground (see Fig. 1). Our three annual species are erect, and although they are many branched, they don't remind me of a spider or spider's web at all.

Although the taxonomy worldwide is difficult, primarily because different species often differ only by small details of the fruit, our four species are easily distinguished. Instead, the problem is finding them! You won't see most of them in bloom during the usual flowering period for desert annuals, and you are unlikely even to see live plants of our three annuals.

Our three annual species are summer annuals, germinating only from warm monsoonal rains of July through September, and sometimes from warm October rains. They grow and flower quickly, and are generally finished by December. Dead remnants persist for at least a few months, but are extremely hard to spot and difficult to identify in their dead form.

Even our perennial species responds best to summer rainfall, producing lush growth and fall / winter flowers when summer rainfall occurs. Otherwise, it mostly doesn't even grow until the weather warms up and most people have left the desert, blooming in April through July. The plant in Fig. 1a didn't receive summer rainfall, and was just beginning vegetative growth in February; the plant in Fig. 1b did (in this case, an early warm October rain), and was blooming in January through March.

Here's a pictorial key to identify our four Boerhavia species. Go through each row, beginning with the first row, until you get the identification of your plant.

Flower color red; plant a prostrate perennial (see Fig. 1), usually with dead stems persisting from the previous year ...B. coccinea
Flower color pinkish-white; plant an erect annual ... continue below
Flowers at tips of at least some inflorescence branches in some plants in an umbel of 3-6 flowers (all individual flower stems originating from a common point), with other terminal branches having a single flower or paired flowers ... B. intermedia
Flowers on most inflorescence branches in a definite spike-like raceme (at least 4 nearly-sessile flowers spaced along the branch) ... continue below
Fruit mostly with 4 ribs;

middle of stem glandular-hairy (other parts of stem can be sticky, glabrous or hairy);

fruit bracts mostly persistent, reaching at least the mid-point of the fruit ... B. wrightii

Fruit mostly with 5 ribs;

stem sticky, glabrous or hairy but not glandular-hairy in any part;

fruit bracts mostly deciduous, shorter than mid-point of fruit when present ... B. coulteri

(Fruit shown is B. intermedia due to lack of good fruit pix for B. coulteri showing the 5 ribs)

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Copyright © 2011 by Tom Chester.
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Updated 9 October 2011