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| Fig. 1. Our two most common Chamaesyce species. Left: C. melanadenia, Mine Wash, 27 January 2011. Right: C. polycarpa, Villager Peak Trail, 8 February 2011.
Note the appressed, thinly tomentose hairs on C. melanadenia, and its showier white appendages ("petals"), compared to the short spreading hairs (or sometimes no hairs at all) on C. polycarpa, and its less showy appendages. Click on the pictures for larger versions. | ||||
Table of Contents
Introduction and Photographs
List of Species, Abundances, Geographic Ranges, Habitat and Monsoon Response
How To Identify Each Species
Introduction and Photographs
We have ten Chamaesyce species in the Borrego Desert Area and the desert area to the south. These are now placed in the genus of Euphorbia, but I continue to use the Chamaesyce name in order to follow the 2012 printed Jepson Manual.
Most of these species are unique enough that they can be identified by sight, or by using a hand lens to check for a distinctive feature.
Fig. 1 shows pictures of each of our ten species, including two different pictures of our most variable species, C. polycarpa. Tips on how to distinguish these species are given below.
The color of the plant is of some significance, but is not reliable. Most Chamaesyce start out green, or yellow-green, and then turn red as they age. Some turn red faster than others, such as C. arizonica, C. serpyllifolia and C. setiloba. C. melanadenia is often purplish.
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| C. abramsiana Blair Valley, 11 October 2013. | C. albomarginata Glorietta Canyon, 27 November 2013. | C. arizonica Henderson Canyon, 6 December 2013. | C. melanadenia Glorietta Canyon, 27 November 2013. |
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| C. micromera Elephant Tree Natural Area, 1 December 2009. | C. pediculifera Fossil Canyon, 23 December 2010. | ||
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| C. polycarpa Alcoholic Pass Trail, 23 February 2010. | C. polycarpa Split Mountain Road, 1 December 2009. | ||
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| C. revoluta Pinyon Mountain Road Area, 10 November 2013. | C. serpyllifolia ssp. serpyllifolia S2, 15 October 2013. | C. setiloba Glorietta Canyon, 5 March 2013. | |
| Fig. 1. Photographs of the ten Chamaesyce species in the Borrego Desert area. Click on the pictures for larger versions. | |||
List of Species, Abundances, Geographic Ranges, Habitat and Monsoon Response
Table 1 lists the species, how common they are, whether they are strictly monsoonal species or not, and their geographic and elevation ranges. The commonness is given numerically by the number of separate areas where we have found each species in our surveys, and also by the number of areas in the desert portion of San Diego County from vouchers.
The geographic range is reported as Widespread if it spans the north-south range of its habitat in San Diego County. A widespread species can be common or uncommon in its geographic range. The elevation range is from our GPS locations and from voucher records.
All Chamaesyce respond strongly to summer rainfall. Five species are only present after monsoonal rain, and have a mark in the column M only. The other five species also respond also to winter / spring rain. Two of those species, C. albomarginata and C. setiloba, respond best to monsoonal rain, and have a mark in the column M best. The others respond well to both monsoonal and winter/spring rain, and have a mark in the column M/S.
The print version of the Jepson Manual Second Edition uses Chamaesyce as the genus name, but the more-recent online flora uses Euphorbia as the genus name. We retain the name Chamaesyce since our policy is to conform to the most recent printed flora, the one mostly likely to be carried in the field.
Table 1. The Chamaesyce Species of the Borrego Desert Area
| Scientific Name | Common Name | # Areas | Geographic Range | Elevation range (ft) | Habitat | Monsoon / Spring | |||
|---|---|---|---|---|---|---|---|---|---|
| Us | V | M only | M best | M / S | |||||
| Chamaesyce abramsiana | Abrams' prostrate spurge | 1 | 8 | Widespread | 0-2600 | Flat sandy areas | X | ||
| Chamaesyce albomarginata | rattlesnake weed | 5 | 23 | Widespread | 1260-4235 | Flattish areas and gentle slopes in areas with significant soil | X | ||
| Chamaesyce arizonica | Arizona spurge | 3 | 4 | Widespread | 1050-3000 | Sandy flats, including flattish areas in desert transition zone near base of mountains | X | ||
| Chamaesyce melanadenia | red-gland spurge | 14 | 33 | Widespread | 1000-5300 | Slopes, flats and washes | X | ||
| Chamaesyce micromera | Sonoran spurge | 15 | 11 | Widespread | 675-4260 | Flat sandy areas | X | ||
| Chamaesyce pediculifera | Carrizo Mountain spurge | 3 | 4 | Only in southern portion of ABDSP, Bisnaga Alta Wash to Mexican border | 700-2000 | Washes, Canyon bottoms | X | ||
| Chamaesyce polycarpa | small-seeded spurge | 50 | 51 | Very widespread | 115-1780 | Dry sandy slopes and sandy flats | X | ||
| Chamaesyce revoluta | rolled-leaf spurge | 1 | 1 | Only present on the north slope of Whale Peak, in Pinyon Mountain Valley | 3800-4600 | Areas with soil in steep rocky slopes | X | ||
| Chamaesyce serpyllifolia ssp. serpyllifolia | thyme-leafed spurge | 6 | 1 | Culp Valley area, Pinyon Mountain Road area | 2525-4600 | Hillsides | X | ||
| Chamaesyce setiloba | starfish spurge, Yuma spurge | 16 | 19 | Widespread | 675-4165 | Flat sandy areas | X | ||
How To Identify Each Species
The characteristics needed to confidently identify each species are shown in Figs. 2 and 3.
Identifying characteristics of the flowers
Fig. 2 labels some of the characteristics of the flowers used for identification.
Fig. 2. Identifying characteristics for Chamaesyce flowers are labeled in the photograph. See the text for explanation.
What most people would call the "petals" are actually called petaloid appendages = petal-like gland appendages. They are not petals since they are not attached to the base of the flower itself as petals are. They are called an appendage because they are attached to ("appended to") the gland. The gland contains nectar for visiting pollinators. The petaloid appendages are useful for identification since they vary quite a bit, from being absent, to small, to large and asymmetric.
The gland is "transversely oblong" (longest in the direction perpendicular to the direction to the tip of the flower) in all species except two species with round glands, C. micromera and C. revoluta. The glands in Fig. 2 are oblong in shape. The color of the glands can vary quite a bit in a single species; Fig. 2 shows a variation from a very light washed-out red/pink to a deep red color with some black.
The parts of the flower are in an involucre. The shape and hairiness of the involucre can be important for identification.
The flowers of Chamaesyce are either male or female, with both sexes found on the same plant, often at the same time. The flowers of all species develop in the same way, and can appear very different depending on their stage.
When female flowers are fresh, the styles are just emerging from the center, following shortly by the ovary emerging. The ovary is on a stalk, and it and the stalk continue to enlarge as the flower develops, giving the appearance of "something green hanging out of the middle of the flower".
Male flowers will have variable number of stamens showing. Usually only a few stamens are present at one time, with others developing at different times in the same flower. Some male flowers look very odd after the pollen is lost, and the anthers elongate.
Identifying characteristics of the leaves and their stipules
Each Chamaesyce leaf generally has a pair of very-short (sometimes minute!) free appendages at the base of the petiole, one on each side of the petiole (see drawing from Wayne Armstrong's Vegetative Terminology page). Since the leaves are opposite, on each side of the stem you can see, with a hand lens, one stipule from each leaf. Sometimes those stipules can become joined together, appearing as only a single fused stipule on each side of the stem.
Fig. 3 shows how different the leaf stipules can appear. The stipules for C. albomarginata are so prominent that they are often able to be seen in photographs targeting the flowers. They are prominent because in this species, the stipules at the base of each of the opposite leaves have become fused to each other along their edges (not fused to the stem) into a wide, very-white scale. If you see a stipule like this on the upper side of the stem, this immediately identifies the plant as C. albomarginata.
In contrast, the stipules on the upper surface of the stem for C. polycarpa are quite hard to see. They are not fused and very narrowly-triangular, almost thread-like. Under a good microscope, one can see that they are ciliate, but this is hard to see with a hand lens in the field. It takes some experience to learn to see these small stipules.
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| Fig. 3. Left: upper stipules for Chamaesyce albomarginata, and the "albo-marginated" leaf blade. Right: upper stipules for C. polycarpa, and its not so "albo-marginated" leaf blade. See the text for explanation. | ||
Stipules are an excellent way to confirm many determinations. Stipules can be fused on both the upper and lower surface; free above and fused below; or free on both the upper and lower surface. Individual stipules can be a single strand, or divided into multiple strands, and be ciliate or not.
Fig. 3 also shows the very prominent differently-colored leaf blade margin for C. albomarginata, that is the source for its species name.
With this terminology now defined, I can now easily give the distinctive characteristics of each species in Table 3.
Table 3. How to Identify the Chamaesyce Species of the Borrego Desert Area
| Scientific Name | Identifying Characteristics | Additional Characteristics |
|---|---|---|
| Chamaesyce abramsiana | One of just two species whose inflorescence is mainly in axillary branches, and the leaves are ~oblong, not round, with short teeth near the tip. The other species is the very similar C. serpyllifolia. See next section to identify it. | Plant is dead prostrate. Stipules free, 2-5 parted. |
| Chamaesyce albomarginata | Only species with wide membranous fused upper (and lower) stipules. The different-colored margin of the leaves is more prominent in this species than in most others. | Plant is usually dead prostrate, with showy gland appendages. |
| Chamaesyce arizonica | Only species whose involucre is urn-shaped, fairly narrow and widest in the middle, instead of bell-shaped, widest near the top. One of just two species with glistening (translucent, not opaque) hairs, the other being C. setiloba. | Plant is not prostrate, and often quite reddish. Stipules are minute, free. |
| Chamaesyce melanadenia | Only species with at least thinly-tomentose hairs, which are hairs that are matted and tangled, soft and a bit woolly. The hairs are on the stem, leaves, involucre, ovary and fruit. Sometimes the hairs aren't quite dense enough to fully qualify as tomentose, but they are still distinctive. The closest other species in hairiness is the hairy form of C. polycarpa, which has spreading hairs, not matted, not tangled, and not woolly. | Plant is usually a rounded mound, often purplish, with showy gland appendages. With practice, this species can be recognized easily from a standing position due to its growth habit. Stipules free above, fused below. |
| Chamaesyce micromera | Only species with no gland appendages One of two species with round glands, the other being the very different E. revoluta. | Plant is dead prostrate. Stipules free above, fused below, ciliate. |
| Chamaesyce pediculifera | Only species with markedly-different-sized gland appendages, with one pair much bigger than the other pair. | Stipules free, thread-like. |
| Chamaesyce polycarpa | One of just three species with stipules free above and fused below. The other two species are: C. melanadenia, which always has tomentose hairs, whereas C. polycarpa either has no hairs at all, or has short spreading hairs; and C. micromera, which has round glands without appendages, whereas the glands of C. polycarpa are oblong and almost always have at least tiny appendages.
Only two other species have spreading hairs, the distinctive C. micromera and C. setiloba. So if you observe spreading hairs, and can rule out those two species, you've got the id. | This species is extremely variable for the size of its gland appendages. Many plants here have almost no gland appendage at all, so small that a dissecting scope is needed to see it clearly. Plants with large showy gland appendages are the coastal form, found mostly at the western edge of the Desert Transition Zone in the Borrego Desert. |
| Chamaesyce revoluta | Only species with linear leaves instead of roundish leaves. | Plant is erect. Stipules free, linear. |
| Chamaesyce serpyllifolia ssp. serpyllifolia | One of just two species whose inflorescence is mainly in axillary branches, and the leaves are ~oblong, not round, with short teeth near the tip. The other species is the very similar C. abramsiana. See next section to identify it. | Plant is not prostrate, usually with ascending stems. Stipules free, linear, entire or divided. |
| Chamaesyce setiloba | Only species with prominently-fringed gland appendages. One of just two species with glistening (translucent, not opaque) hairs, the other being C. arizonica. | Plant is prostrate. Stipules free, thread-like. |
Identifying C. abramsiana and C. serpyllifolia ssp. serpyllifolia
These two species have an inflorescence consisting of dense axillary branches, very different from the inflorescence of the other eight species which have single flowers in the axils of the leaves on their stems, with no axillary branches (although the stems are generally repeatedly forked). Fig. 4 shows the inflorescence habit of each species.
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| Fig. 4. Left: inflorescence of Chamaesyce abramsiana. Right: inflorescence of Chamaesyce serpyllifolia ssp. serpyllifolia | ||
The easiest way to discriminate these species is that C. abramsiana forms dense prostrate mats, whereas in our area C. serpyllifolia ssp. serpyllifolia is a much more open plant with ascending stems, as shown in Fig. 5. However, west of the mountain crest, plants of C. serpyllifolia ssp. serpyllifolia can also be prostrate.
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| Fig. 5. Plant habit of Chamaesyce abramsiana (left) and Chamaesyce serpyllifolia ssp. serpyllifolia (right). | ||
Nathan Tayler has pointed out that the stems of C. serpyllifolia ssp. serpyllifolia tend to be ribbed or winged, compared to the smooth stems of C. abramsiana, as seen most clearly in Fig. 6.
There are two other differences, which need a microscope to see reliably. Chamaesyce serpyllifolia ssp. serpyllifolia has no hairs at all, whereas Chamaesyce abramsiana has at least some hairs in the plants we've observed. (Jim Andre has found a few plants of Chamaesyce abramsiana in the eastern Mojave that have no hairs.) The stipules of C. serpyllifolia are linear, entire or divided, whereas the stipules of C. abramsiana are 2-5 parted.
Both of these two differences are shown in Fig. 6.
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| Fig. 6. Stem hairs and stipules for Chamaesyce abramsiana (left) and Chamaesyce serpyllifolia ssp. serpyllifolia (right). | ||
I thank Jay Keller for alerting me about Nathan Taylor's observations that the stems C. serpyllifolia ssp. serpyllifolia are ribbed or winged, and for Jay's observation that this species has a tendency to be prostrate west of the mountain crest.
I especially thank Nathan Taylor for catching an erroneous determination I had previously on this page, where in 2012 I had mistaken a plant of C. arizonica as a showy C. polycarpa, as well as the tip about only C. arizonica and C. setiloba having glistening hairs.