Eastern Mojave Vegetation Tom Schweich
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Eastern Mojave Vegetation | Two occurrences of Desert Elkweed Swertia albomarginata (S. Watson) Kuntze Gentianaceae in the Mid Hills, Eastern Mojave Desert, San Bernardino County, California |
| Tom Schweich |
Topics in this Article: Introduction Literature Review Field Work and Methods Results Taxonomy Distribution Growth Habits Relationships to Soils and Other Plants Life History Discussion Summary Literature Cited Appendix A -- Field Data Communications Received. |
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|  Swertia albomarginata, rosette of leaves.
Other Articles: Eastern Mojave Geology: Winkler Formation Winkler Formation Giant Ledge Mine Vegetation of the Mid Hills: Measured Plots | IntroductionDesert Elkweed (Swertia albomarginata) is a pretty little plant which is found occasionally in Pinyon-Juniper woodlands of southwestern USA deserts. It grows low to the ground with a rosette of green leaves that have white edges. The white flowers with purple spots are borne on 3-4 dm (12-16 in) stalks. |
Desert Elkweed grows for more than one year which makes it a perennial. However, it does not form wood like a tree does, so it is called an herb. The only permanent part of the plant is the root, and the top of the root, where the leaves and flower stem grows, is called a caudex.
| |  Swertia albomarginata with flower stem.
Other Articles: Glossary: rosette
The leaves of S. albomarginata grow in a circular pattern around the top of the caudex, in what is called a rosette. You can see the rosette in the photograph at left. The leaves have a small white edge, or margin, around the green leaf and that is how the plant got its name: albomarginata. Albo- means "white" and -marginata means "margined" so the scientific name Swertia albomarginata could mean "White-margined Swertia." The genus name of Swertia, by the way, is named for E. Sweert, a Dutch herbalist, who was born in 1552.
| | Other Articles: Glossary: whorl
When S. albomarginata flowers it sends up a stem which is 8 to 24 inches (2-6 dm) tall and has very thin leaves aranged around the stem in a whorl>.
| |  Swertia albomarginata infloresence. Other Articles: Glossary: glabrous
The stem and all the leaves are smooth and shiny, and do not have hairs, prickles (like roses), or glands (like sundews) on them, and so the plant is said to be glabrous. There are some S. albomarginata in the mountains near Las Vegas, Nevada, that have a thin covering of sticky cobwebby hairs, but these are thought be a a separate subspecies.
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 Swertia
albomarginata flower. Other Articles: Glossary: monocarpic semelparous
The flowers are about 1 inch (2.5 cm) in diameter, with greenish white petals that have purple dots. Nectar, to attract pollinating insects, is secreted in pits which are located well out on the petals, as can be seen in the photograph at left. S. albomarginata flowers only once in its life history and then dies, and is therefore called semelparous, or monocarpic.
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A typical description of Desert Elkweed S. albomarginata in a scientific publication would say:
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| Desert Elkweed (S. albomarginata) is a semelparous perennial 2-6 dm high, a single-stemmed, glabrous herb with a basal rosette of leaves having a distinctive white margin, and very thin, 1 cm. wide whorled stem leaves. The flowers are greenish-white with purple dots and are borne on slender branches. Each petal has an oblong nectary pit which is fringed and wider or two-lobed at the tip. | Literature Cited: The species (i.e., Swertia
albomarginata; it is common in botanical literature to refer to a species being described by simply saying, "the species." This avoids having to spell out Swertia albomarginata every time the species is referred to.) is known from the California desert mountains through southern Nevada, northern Arizona and southern Utah to Colorado (Hickman, 1993). Its Colorado range is quite limited, being known only from Montezuma County in extreme southwestern Colorado. There are several other species of Swertia in southwestern American deserts, but it is unlikely that the species will be confused.
| | Literature Cited: Common names for the
species are "Mojave gentian" (DeDecker, 1984), "White-margined Swertia" (Welsh et al., 1987), "White-margined Frasera" (Albee, Shultz and Goodrich, 1988) and "Desert Elkweed" (Kartesz, 1988).
| | Locations: Pinto Mountain. Wild Horse Mesa.
In the Mid Hills of the eastern Mojave Desert, Swertia albomarginata is found on the north face of Wild Horse Mesa and on the south face of Pinto Mountain.
| |  Location of Swertia
albomarginata on the north slope of Wild Horse Mesa. 
North slope of Wild Horse Mesa. Other Articles: Wild Horse Canyon Road: North Slope of Wild Horse Mesa Locations: Wild Horse Mesa. The location of the
Wild Horse Mesa site is shown in the map at left, on the north face of Wild Horse Mesa at 1550-1600 m, west of Wild Horse Canyon Road, associated with Pinus monophylla and Juniperus osteosperma. The soil is white, and has been informally called the "Winkler Formation." See the section on "Soil Relations" below. Much of the area has been disturbed and there are numerous old roads that were presumably constructed to support former mining activities. The area is now designated a wilderness area. By GPS receiver, the location is N 35° 02.889' W 115° 27.458'. The species is found at other locations on the north face of Wild Horse Mesa, wherever the Winkler formation crops out.
| |  Pinto Mountain across
Round Valley as seen from Black Canyon Road. Other Articles: Cedar Canyon Road: Winkler Formation Locations: Pinto Mountain. The location of the Pinto Mountain
site is shown in the photograph at left. It is on the south side of Pinto Mountain at 1660 m elevation, north of Cedar Canyon Road, associated with Juniperus osteosperma. Like the Wild Horse Mesa site, the soil is white, being derived from the Winkler Formation, and quite loose. By GPS receiver, the location is N 35° 10.549' W 115° 23.237'.
| |  Location of one
experimental plots in Swertia albomarginata.
The species has also been reported
at the Quail Rock Ranch near the Pinto Mountain location (Adrienne Knute, personal communication, 1995) and in Caruthers and Keystone Canyons of the New York Mountains, as well as the marine limestones of Clark Mountain (A. Romspert, personal communication, 1995).
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| Literature ReviewThere is very little published about Swertia albomarginata, other than descriptions in the various floras. | Literature Cited: Post's (1956) dissertation on the
Frasera and Swertia of North America contains perhaps the most data of any kind available on the species. There is a lengthy description of the species and a review of synonymy.
| | Literature Cited: Post's (1958) paper on the nodal
anatomy of Frasera and Swertia perennis is a further elaboration of work begun in his dissertation. In this study he examined three S. albomarginata. Post's (1958) comments add little to understanding of the ecology of S. albomarginata. He does note, however, that "... F. gypsicola (unilacunar) and F. albomarginata (trilacunar) were found together on "gypsum" dunes along the White River in an arid region of central Nevada." Post (1958) also suggests some interspecies relationships in his comments, "... the phyllotaxy in F. gypsicola is opposite, wheras F. tubulosa has whorled leaves, as does on of the trilacunar species, F. albomarginata, with which it appears to have its closest affinity."
| | Literature Cited: Pringle's (1990) taxonomic notes on
western American Gentianaceae are intended to explain the treatment of Frasera and Swertia in The Jepson Manual (Hickman, 1993) of the flora of California. Unfortunately, Pringle (1990) makes no comments about S. albomarginata.
| | Literature Cited: Beattle, Breedlove
and Ehrlich (1973) reported their results with the better-studied and well-known Swertia radiata (=Frasera speciosa), commonly known as Monument Plant.
| | Literature Cited: Taylor and Inouye
(1985) followed populations of Swertia radiata for 9 years in a study much like the present one. Since the flowers of S. radiata and S. albomarginata are very similar, there may be some similarity in life history and pollination biology. However, any similarity would be validated through field studies.
| | Literature Cited: Chassot et al. (2001) …
| | Literature Cited: Chassot (2003) … |
| Literature Cited: Xue, et al. (2007) …
| | Literature Cited: Yuan, et al. (2003) …
| | Literature Cited: von Hagen and
Kadereit (2002) … | | Literature Cited: Some semelparous
desert plants are capable of clonal reproduction. Tissue and Nobel (1990) studied Agave desertii, an agave whose northern range overlaps slightly with Swertia albomarginata, a semelparous species that exhibits clonal reproduction.
| | Literature Cited: LeBuhn (2004) … studies
Ipomopsis longiflora (Torr.) V. Grant subsp. australis, a Chihuahuan desert annual that has two discrete flowering seasons.
| | Literature Cited: Huxman and Loik
(1997) … studied two varieties of Yucca whipplei … one which is primarily semelparous and one primarily iteroparous …
| | Literature Cited: Metcalf, Jessica C.,
Karen E. Rose, and Mark Rees (2003) … Monocarpic plants, which flower once then die, are ideal systems for testing evolutionary ideas because the cost of reproduction is easily quantified and the timing of flowering is a key determinant of darwinian fitness.
| | Literature Cited: Kamenetsky (1994) … Analyses of
life cycle, morphogenesis of the monocarpic shoot, and propagation have been carried out on Allium rothii, a desert geophyte from the Western Irano-Turanian region.
| | Literature Cited: Hegazy (2000) … Verbascum
sinaiticum Benth. (Scrophulariaceae) is a biennial rosette plant. The species is rare in Egypt and its distribution is restricted to the Sinai peninsula. The investigated population was located in Saint Catherine, Southern Sinai.
| | Literature Cited: Hegzy [Hegazy?] …
Autecology of the desert monocarpic Rumex cyprius as influenced by water treatment
| | Literature Cited: Gross (1984) … Effects of Seed Size
and Growth Form on Seedling Establishment of Six Monocarpic Perennial Plants
| | Literature Cited: Hegazy and Kabiel
(2007) … microhabitat heterogeneity in the spatial pattern and size-class structure of Anastatica hierochuntica L.
| | Literature Cited: Burd, et al. (2006) …
AGE–SIZE PLASTICITY FOR REPRODUCTION IN MONOCARPIC PLANTS |
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| | Date and time this article was prepared: 5/8/2008 9:42:54 AM |