Desert yellowhead is a tap-rooted perennial herb. The entire plant is smooth, possessing no hair or other projections. The stems have leathery leaves and grow up to 11.8 inches tall. The leaves grow in an alternating pattern and are often folded along the vein in the middle of the leaf. Flower heads are numerous (25 to 180) and crowded on top of the stem. Each flower head contains four to seven yellow disk flowers (ray flowers are absent) surrounded by four to seven yellow, keeled involucral bracts (modified leaves below the flower head). The seeds have tufts of white hairs (Dorn 1991, pp. 198-201; Heidel 2002 pp. 4-7).

This species was originally described as a classic ‘K’- selected species (instead of ‘R’-selected, with many offspring and short lifespan), characterized by a long-lived perennial growth form, adaptation to severe habitats and low annual reproductive output (Fertig 1995, p. 19). However, Scott and Scott characterized desert yellowhead as being an S-R strategist (from the C-S-R Triangle from the universal adaptive strategy theory of plants’ strategies of competitor, stress tolerator and ruderal). That is, ‘S’ for stress-tolerant and capable of surviving in disturbed habitats and ‘R’ for ruderal, meaning an early colonizer and adapted to habitats that are severe to extreme (Scott and Scott 2009, p. 58).

Desert yellowhead most likely follows the typical life history of an herbaceous perennial vascular plant: seeds germinate and become seedlings, seedlings survive and become vegetative plants, vegetative plants survive to flower, flowering plants reproduce sexually and produce seeds, and flowering can repeat whether the individual was vegetative or flowering the previous year. Plants also reproduce vegetatively by production of and differential survival of ramets, or asexually reproduced plants formed from the budding of modular plants at both the vegetative and flowering life stages (Fertig 1995, p. 17). Evidence of this modular growth exists based on the branching patterns observed in mature plants (Scott and Scott 2009, pp. 11-12) and by the number of new non-seedling plants observed year-over-year (Doak et al. 2016, p. 25). Assumptions regarding some life history traits, such as inference that the formation of ramets occurs regularly in desert yellowhead, are based on the best available information.

New plants established from seed or ramet grow for multiple years before flowering, and after first flowering often have years in which no flower production occurs (Doak et al. 2016, p. 4). Plants require the development of a basal cluster of leaves before flowering occurs (Scott and Scott 2009, p. 41). Based on one long-term demographic study, flowering may take place after the plant has grown for a minimum of five years (Scott and Scott 2009, p. 47). Plants can live 21 or more years (Scott and Scott 2009, p. 47). Because of high levels of seedling mortality, the average lifespan may be much shorter, except for established plants. Lifespan can also be higher if one considers the differential survival of ramets that are genetically identical to the original plant and live after the original plant has died.

Desert yellowhead (Yermo xanthocephalus) is a federally threatened perennial herb (67 FR 11442; March 14, 2002) that is endemic to the Beaver Rim area on the western edge of the Sweetwater Plateau and Wind River Basin in southern Fremont County, Wyoming.  There are two populations that are approximately 5 miles apart. 

Desert yellowhead is a tap-rooted perennial herb. The entire plant is smooth, possessing no hair or other projections. The stems have leathery leaves and grow up to 11.8 inches tall. The leaves grow in an alternating pattern and are often folded along the vein in the middle of the leaf. Flower heads are numerous (25 to 180) and crowded on top of the stem. Each flower head contains four to seven yellow disk flowers (ray flowers are absent) surrounded by four to seven yellow, keeled involucral bracts (modified leaves below the flower head). The seeds have tufts of white hairs (Dorn 1991, pp. 198-201; Heidel 2002 pp. 4-7).

The entire known range of desert yellowhead consists of two populations on BLM-managed land in southern Fremont County, Wyoming. The Sand Draw population consists of a main patch and three smaller patches, which occur on approximately 74  acres. The Cedar Rim population consists of 10 patches and occurs in an area of less than 1.2 acres. However, this species’ total physical occurrence footprint covers an area of less than 11.9 acres, making the species potentially vulnerable. The habitats of the two populations differ not only in their topographic positions, but also in vegetation structures (Heidel et al. 2011, pp. 2 and 20). The occupied habitat of the Sand Draw population of desert yellowhead is mainly in shallow depressions created by erosion in outcrops of Miocene sandstones and limestones of the White River Formation (Van Houten 1964, pp. 54–78) at approximately 6,750 feet of elevation. These depressions accumulate drifting snow and may be more moist than surrounding areas. At Sand Draw, desert yellowhead is also found on very steep erosive slopes and old road cuts. The vegetation of these sites is typically sparse, with less than 10 percent cover, and consists primarily of low cushion plants and scattered clumps of Indian ricegrass (Oryzopsis hymenoides; Fertig 1995, p. 24).

By comparison, the Cedar Rim population is restricted to a narrow band along upper to lower escarpment slopes that are generally south-facing on gravelly silt loam derived from White River Formation at approximately 7,080 feet of elevation, which is approximately 330 feet higher than the Sand Draw population. The vegetation at Cedar Rim is “mostly at ecotone [transition] between cushion plant rim and sagebrush sagebrush
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This species was originally described as a classic ‘K’- selected species (instead of ‘R’-selected, with many offspring and short lifespan), characterized by a long-lived perennial growth form, adaptation to severe habitats and low annual reproductive output (Fertig 1995, p. 19). However, Scott and Scott characterized desert yellowhead as being an S-R strategist (from the C-S-R Triangle from the universal adaptive strategy theory of plants’ strategies of competitor, stress tolerator and ruderal). That is, ‘S’ for stress-tolerant and capable of surviving in disturbed habitats and ‘R’ for ruderal, meaning an early colonizer and adapted to habitats that are severe to extreme (Scott and Scott 2009, p. 58).