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You are here >1Up Info > Wildlife, Animals, and Plants > Plant Species > Shrub > Species: Gutierrezia microcephala | Threadleaf Snakeweed
 

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BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Gutierrezia microcephala | Threadleaf Snakeweed
GENERAL BOTANICAL CHARACTERISTICS : Threadleaf snakeweed is a small, native, resinous, perennial desert subshrub that is typically less than 1.6 feet (0.5 m) in height and less than 3.3 feet (1 m) in canopy diameter. It has many erect herbaceous stems which arise from woody basal stems and die back annually [16,27,30,40]. The herbaceous stems are photosynthetic, giving the plant a high photosynthetic capacity [24]. A mature plant with an 8- to 12-inch (20-30 cm) canopy diameter has 100 to 200 photosynthetic stems [30]. The seedling taproot becomes more extensive and diffuse with age [24]. Root length of mature plants averages 6.9 inches (17.4 cm) [25]. Threadleaf snakeweed generally lives less than one decade; maximum age observed in a New Mexico grassland was 18 years [30]. Threadleaf snakeweed exhibits some degree of summer deciduousness. In the Mojave Desert in western Arizona, total threadleaf snakeweed canopy in early August was 54 percent of the maximum biomass observed in spring [8]. RAUNKIAER LIFE FORM : Chamaephyte Phanerophyte REGENERATION PROCESSES : Threadleaf snakeweed produces many seeds [30,33]. Wind dispersal of seeds is inefficient because of a highly reduced pappus, so most seeds fall within a few meters of the parent plant [30]. Seeds are dormant and require a 4- to 6-month afterripening period. After 6 months, maximum germination occurs at a constant temperature from 59 to 77 degrees Fahrenheit (15-25 deg C) with an 8-hour light period. Light enhances germination, suggesting that germination is favored at or near the soil surface [22]. In a New Mexico grassland, seeds germinated abundantly where the established vegetation had been experimentally removed [30]. Germination is also enhanced by winter and spring precipitation [29]. Seedlings produce a single stem and a taproot. A yearling has three to four stems. Several years are required before seeds are produced [30]. The duration of threadleaf snakeweed seed viability in soil is unknown [25]. Parker [30] found an average of 24.2 viable seeds per square meter in the soil of an arid grassland site in New Mexico. Seedling abundance was not noticeably depressed in the spring following a year in which insect herbivory destroyed the seed crop [30]. Parker [30] found considerable year-to-year fluctuation in plant recruitment. Threadleaf snakeweed is vulnerable to local extinction because seedlings frequently succumb to drought, grasshopper defoliation, and competition from grasses [30]. In an arid New Mexico grassland, seedling survival was five times greater where competing vegetation had been removed than on undisturbed sites. In a year of abundant grasshoppers (Hesperotettix viridis), predation on threadleaf snakeweed seedlings was reduced when mature threadleaf snakeweed plants were nearby because the grasshoppers generally hopped from one mature threadleaf snakeweed canopy to another and rarely moved among seedlings at ground level [29]. According to Mayeux and Leotta [22], threadleaf snakeweed reproduces solely by seed. One reference from a study in New Mexico described a very low rate of sprouting from the root crown after mature plants were clipped to ground level [29]. SITE CHARACTERISTICS : Threadleaf snakeweed occurs in desert climates [8]. In southwestern Utah, threadleaf snakeweed is preferentially associated with xeroriparian sites which have higher annual moisture than uplands but running water only on infrequent occasions [23]. It primarily occurs on well-drained, sandy, gravelly, or rocky soils [4,16,28,41]. It is often found in washes or on adjacent slopes [8]. Threadleaf snakeweed often predominates on southern exposures with shallow rocky soils where grasses are not well established [4]. Elevational ranges by state are as follows: Arizona 3,500 to 6,500 feet (1,100-2,000 m) [18] California 5,900 to 8,200 feet (1,800-2,500 m) [16] Colorado 4,000 to 8,000 feet (1,200-2,400 m) [12] Texas 2,500 to 6,000 feet (760-1,800 m) [31] Utah 2,800 to 6,000 feet (850-1,830 m) [40] Although the ranges of the two perennial snakeweeds overlap, they appear to occupy slightly different niches. Threadleaf snakeweed was more prevalent than broom snakeweed on drier upper slopes along a vegetation transect in the Chihuahuan Desert, New Mexico [41]. However, in southwestern Utah, threadleaf snakeweed occupied the lower slope and floodplain while broom snakeweed occupied the upper slope and ridgetop [3]. SUCCESSIONAL STATUS : Facultative Seral Species Threadleaf snakeweed is probably intolerant of shade since it rarely occurs in the presence of a woody overstory [25]. It pioneers on disturbed sites and overgrazed rangeland [28,20,31,38]. In San Bernardino County, California, threadleaf snakeweed was present in low numbers on a pipeline construction zone 12 years after the disturbance [38]. Perennial snakeweed populations are often cyclic, dying back when conditions for seedling establishment are unfavorable and then reappearing when conditions are favorable [24]. Prolific seed production and buried seeds permit opportunistic seedling recruitment during favorable periods. Once established on a site, threadleaf snakeweed may persist numerous generations despite a short life span, poor seedling recruitment during some years, and intense competition from grasses [30]. SEASONAL DEVELOPMENT : New terminal growth begins on basal stems from January through March. Flowering is initiated in the spring and early summer, but plants become dormant during summer drought and do not bloom until late summer or fall. Twig dieback occurs in late fall after flowering [8,33]. Flowering phenology depends on yearly climatic conditions; blooms last longer in wet years [33]. Germination occurs in early spring [30].

Related categories for Species: Gutierrezia microcephala | Threadleaf Snakeweed

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Information Courtesy: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Fire Effects Information System

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