Plant Species of the Borrego Desert: Fabaceae: annual Lupinus species, Lupines

Two forms of Lupinus concinnus growing intermixed in Bitter Creek Canyon, 15 April 2011. The pictures are roughly to the same scale; see also picture with both forms in them. Click on the pictures to get larger versions.

Some lupine species are very distinctive, whereas others are taxonomic nightmares, in which even DNA has trouble separating them. This is true both for the shrubby species and the annual species. Many of these species are so difficult to tell apart that taxonomic keys often make use of miniscule characters that are hard to observe in order to try to reliably separate them, such as whether the hidden keel of the flower contains minute hairs at one end or the other (see labeled picture), and whether the back of the banner has a handful of nearly-invisible hairs or not. Neither of those characters are visible in typical photographs of the flowers.

This page presents just the annual lupine species found in the desert section of Anza-Borrego Desert State Park below 3000 feet elevation, which are the only lupine species we have, except for a small number of plants of L. excubitus var. medius in the southern part of the Park.

Using the taxon delineations in the Jepson Manual, both first and second editions, we have seven species of annual lupines, one of which has two subspecies, making a total of eight taxa. However, if one uses the taxon delination in the 1974 Munz Flora of southern California, we have nine species of annual lupines, and a total of 14 taxa! Furthermore, one of our annual lupine species comes in two forms that are different enough that most people think they are different taxa, which would make a total of 15 taxa if those are counted as two taxa.

The difference between the Munz (and Beauchamp) treatment and the Jepson Manual treatment is that the Jepson Manual combined six of the Munz taxa under one species name, Lupinus concinnus, and combined two of the L. sparsiflorus subspecies under just the species name. The Jepson Manual treatment for L. concinnus comments that this species is highly variable, generally self-pollinated, needs study; named vars. ± indistinct; plants in D with linear, coarsely hairy leaflets, ± ciliate lower keel margins may be confused with Lupinus sparsiflorus.

Note that this comment does not say that "these varieties look similar"; it only says at least some specimens are hard to determine to one of the named varieties. In fact, some of these varieties are so strikingly different that when botanists encounter some of the different forms of L. concinnus, their initial reaction is total disbelief that those forms can be called the same name as the previous forms they have encountered.

The additional comment is an alert that it is difficult to separate some forms of L. concinnus from L. sparsiflorus, and that the Jepson Manual key will not correctly determine those plants. And in my experience, that comment should be extended to plants with non-linear leaves as well; ciliate keels are apparently more widespread in L. concinnus than had been thought. I originally misdetermined plants of L. concinnus in Borrego Palm Canyon because they had ciliate keels and obovate leaves. It was only in collecting pictures for this page that I found I had been misled by the key to determine these plants as L. sparsifolius.

It may even turn out on further study that some of these forms of L. concinnus might be placed as a variety under L. sparsiflorus, or it might be discovered that some forms are hybrids between the two species.

The main purpose of this page is to show some of the extreme variability encompassed under the name of L. concinnus to make field botanists aware of this variation, and to help me and my colleagues compare plants we find to what we have seen before here. This page will eventually discuss and show pictures of the other annual species as well. (For now, see the Munz / Beauchamp key for the 14 taxa of annual lupines given in Munz / Beauchamp that are found in the desert section of Anza-Borrego Desert State Park below 3000 feet elevation.)

The forms of L. concinnus recognized in Munz 1974 and Beauchamp 1986

The six taxa that were combined into just the species name of L. concinnus in the Jepson Manua are given in Table 1, along with their distinguishing characteristics and locations in the Anza-Borrego Desert. Var. brevior was given as the species L. brevior in Munz, and var. pallidus was given as the species L. pallidus in both Munz and Beauchamp.

Table 1. The forms of L. concinnus recognized in Munz 1974

Variety NameDistinguishing Characteristics1ABDSD and other Locations from Beauchamp 1986Flowering Time
agardhianusleaflets linear-spatulate, mostly subglabrous above; plants sparsely spreading-pilose; flowers bluish-purpleBorrego Palm Canyon; Banner; Grapevine Spring: Box Canyon, coastal and foothillMar-May
breviorplant glabrous or sparsely pilose; leaflets glabrous above, truncatish; keel ciliate; flowers whorled, ~6 mm long, off-white to bluish or purplishSentenac lupine. infrequent, sandy places, desert, below 700 m, in Creosote Bush Scrub; Borrego Palm Canyon; Scissors Crossing; Wagon Wash; lower Box Canyon; Mountain SpringsApr-May
concinnusleaflets 1.5-3 mm wide; flowers 7-9 mm longoccasional, sandy places; foothill, 400-1200 m; San Felipe Valley; BannerApr-May.
optatusleaflets 4-7 mm wide; flowers 9-11 mm longfrequent, on granitic slopes; foothill and montane, above 400 m; Scissors Crossing; Vallecito Stage StationMar-May
orcuttiileaflets 4-7 mm wide; flowers 6-8 mm longinfrequent, on rocky slopes, 700-1100 m; San Felipe Valley; Culp Valley; Montezuma View Point; Vallecito Valley; Mountain SpringsMar-Apr.
palliduskeel ciliate; plant silky to strigose; leaflets pubescent on both sides; petals pale blue to whitish or yellowish, 5-7 mm longuncommon, sandy areas, desert, below 800 m; Borrego Palm Canyon; San Felipe; Vallecito Station; Carrizo CreekMar-Apr.

1Except as mentioned, all of the taxa are densely hairy on their stems and leaves, have a glabrous keel, and have non-whorled flowers that are pinkish-white to lavender.

Remember, these varieties were said to be ± indistinct in the Jepson Manual treatment, and so you should not expect that a given plant will fit neatly into a single one of these varieties!

Note that three of these varieties are said to be present at Borrego Palm Canyon, vars. agardhianus, brevior and pallidus. One wonders if the same plants were vouchered at different times as those different varieties. The plants from Borrego Palm Canyon fit agardhianus best for the hairiness, leaf shape and flower color, but they have a ciliate keel, which fits the other two varieties. In fact, as mentioned above, I took these plants to be L. sparsiflorus at first, from the ciliate keel, using the Jepson Manual key.

Furthermore, we occasionally find plants of L. concinnus growing right next to each other with a pretty dramatic variation in leaf hairiness and color. One example is given in the pictures at the top of this page.

Distinguishing L. concinnus and L. sparsiflorus

There is apparently no single foolproof way to distinguish these species, since there are versions of L. concinnus that can be confused with L. sparsiflorus. In particular, as mentioned above, the Jepson Manual key fails to properly determine plants of L. concinnus with a hairy keel.

The following is a suite of characters that should distinguish most specimens:

Pictures of L. concinnus and L. sparsiflorus

Click on the thumbnails to get a larger version of each pix.

Fig. 2. Pictures of L. sparsiflorus and two forms of L. concinnus

CharacteristicL. sparsiflorusL. concinnus less-hairy form like agardhianus (leaves nearly glabrous above)L. concinnus densely-hairy form like orcuttii (smaller flowers, wider leaves)
LocationScissors CrossingHenderson CanyonMine Canyon
Entire plant
Leaf
Inflorescence

Fig. 3. Pictures of three more forms of L. concinnus (two from locations outside the Borrego Desert)

CharacteristicL. concinnus var. concinnus (small flowers, small leaves)L. concinnus var. pallidus (ciliate keel; plant silky to strigose)L. concinnus var. optatus (large flowers, large leaves)
LocationWilson Trail, Pinyon Ridge, above Culp Valley, Anza-Borrego Desert State ParkMurray Canyon, Indian Canyons, near Palm SpringsDripping Springs Trail, Agua Tibia Mountain, Palomar Mountain
Entire plant
Leaf
Inflorescence


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Copyright © 2012 by Tom Chester.
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Comments and feedback: Tom Chester
Updated 30 April 2012