Index of Species Information
SPECIES: Gutierrezia microcephala
SPECIES: Gutierrezia microcephala
AUTHORSHIP AND CITATION :
Carey, Jennifer H. 1994. Gutierrezia microcephala. In: Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station,
Fire Sciences Laboratory (Producer). Available:
Revisions : On 17 February 2016, the common name of this species was changed
from: small-head snakeweed
to: threadleaf snakeweed.
Xanthocephalum microcephalum (DC.) Shinners [31,40]
SCS PLANT CODE :
COMMON NAMES :
The currently accepted scientific name for threadleaf snakeweed is
Gutierrezia microcephala (DC.) Gray (Asteraceae) [16,18,27,31,39,40].
There are no currently accepted infrataxa.
This report refers to threadleaf snakeweed and its more common relative,
broom snakeweed (Gutierrezia sarothrae) together as perennial
LIFE FORM :
FEDERAL LEGAL STATUS :
No special status
OTHER STATUS :
DISTRIBUTION AND OCCURRENCE
SPECIES: Gutierrezia microcephala
GENERAL DISTRIBUTION :
Threadleaf snakeweed occurs in the Chihuahuan, Sonoran, Mojave, and
Great Basin deserts of the southwestern United States and northern
Mexico. It occurs from southwestern Texas; north to extreme
southwestern Colorado and south-central Utah; west to southern
California; and south to the Mexican states of Sonora, Chihuahua, and
FRES21 Ponderosa pine
FRES30 Desert shrub
FRES33 Southwestern shrubsteppe
FRES35 Pinyon - juniper
FRES40 Desert grasslands
AZ CA CO NV NM TX UT MEXICO
BLM PHYSIOGRAPHIC REGIONS :
3 Southern Pacific Border
6 Upper Basin and Range
7 Lower Basin and Range
12 Colorado Plateau
13 Rocky Mountain Piedmont
KUCHLER PLANT ASSOCIATIONS :
K019 Arizona pine forest
K023 Juniper - pinyon woodland
K040 Saltbush - greasewood
K053 Grama - galleta steppe
K054 Grama - tobosa prairie
K057 Galleta - three-awn shrubsteppe
K058 Grama - tobosa shrubsteppe
K059 Trans-Pecos shrub savanna
SAF COVER TYPES :
SRM (RANGELAND) COVER TYPES :
HABITAT TYPES AND PLANT COMMUNITIES :
Threadleaf snakeweed occurs in arid grassland and desert shrub
communities. In an arid grassland in New Mexico, threadleaf snakeweed
occurs with galleta (Hilaria jamesii), sand dropseed (Sporobolus
cryptandrus), black grama (Bouteloua eriopoda), and ring muhly
(Muhlenbergia torreyi) . Other desert associates include Joshua
tree (Yucca brevifolia), Nevada ephedra (Ephedra nevadensis), cholla
cactus (Opuntia spp.), and Mojave desertrue (Thamnosma montana) [3,4].
SPECIES: Gutierrezia microcephala
IMPORTANCE TO LIVESTOCK AND WILDLIFE :
Threadleaf snakeweed is poisonous to livestock, especially when it is
growing on sandy soils. It contains saponins and other chemicals that
cause abortions in cattle. Clinical signs of threadleaf snakeweed
poisoning are described [24,34].
Threadleaf snakeweed has very little known value to wildlife . It
may provide cover for small animals, and wildlife may eat the seeds.
Perennial snakeweeds are generally unpalatable to cattle [12,25] except
in early spring when other forage is lacking .
NUTRITIONAL VALUE :
COVER VALUE :
VALUE FOR REHABILITATION OF DISTURBED SITES :
OTHER USES AND VALUES :
OTHER MANAGEMENT CONSIDERATIONS :
Threadleaf snakeweed invades and is an indicator of overgrazed and
disturbed rangelands [9,31]. Once established, threadleaf snakeweed
biomass can exceed 1,000 pounds per acre and reduce grass production to
less than 100 pounds per acre . In 1987 approximately 22 percent of
Texas rangelands were infested with perennial snakeweeds .
Threadleaf snakeweed persists after grazing ceases  so it may
threaten diversity in native plant communities as well as decrease
Various herbicide application techniques have been tested on perennial
snakeweeds. Picloram and triclopyr give satisfactory control .
Picloram is most effective at controlling threadleaf snakeweed when
applied after fall flowering but before new terminal growth begins.
Control lasts at least 5 to 7 years under proper grazing management
. The percent canopy reduction of threadleaf snakeweed was
substantially greater when herbicide was applied during the spring of an
above-average rainfall year than in a drought year .
Biological control of perennial snakeweeds is currently under study
[9,10]. A root-boring weevil from Argentina, closely related to the
native cerambycid root borer (Crossidius pulchellus), was released in
the late 1980s in Texas and New Mexico; the release marks the first
attempt to control a native weed with a foreign insect . The native
cerambycid root borer is not useful for biological control because it
feeds only on large, mature plants, and damage is sporadic [10,30].
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Gutierrezia microcephala
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 . A mature plant with an 8- to
12-inch (20-30 cm) canopy diameter has 100 to 200 photosynthetic stems
. The seedling taproot becomes more extensive and diffuse with age
. Root length of mature plants averages 6.9 inches (17.4 cm) .
Threadleaf snakeweed generally lives less than one decade; maximum age
observed in a New Mexico grassland was 18 years .
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 .
RAUNKIAER LIFE FORM :
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 . 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 . In a New Mexico grassland, seeds germinated
abundantly where the established vegetation had been experimentally
removed . Germination is also enhanced by winter and spring
Seedlings produce a single stem and a taproot. A yearling has three to
four stems. Several years are required before seeds are produced .
The duration of threadleaf snakeweed seed viability in soil is unknown
. Parker  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 .
Parker  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 . 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 .
According to Mayeux and Leotta , 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 .
SITE CHARACTERISTICS :
Threadleaf snakeweed occurs in desert climates . 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 . 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 . Threadleaf snakeweed often
predominates on southern exposures with shallow rocky soils where
grasses are not well established .
Elevational ranges by state are as follows:
Arizona 3,500 to 6,500 feet (1,100-2,000 m) 
California 5,900 to 8,200 feet (1,800-2,500 m) 
Colorado 4,000 to 8,000 feet (1,200-2,400 m) 
Texas 2,500 to 6,000 feet (760-1,800 m) 
Utah 2,800 to 6,000 feet (850-1,830 m) 
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 . However, in
southwestern Utah, threadleaf snakeweed occupied the lower slope and
floodplain while broom snakeweed occupied the upper slope and ridgetop .
SUCCESSIONAL STATUS :
Threadleaf snakeweed is probably intolerant of shade since it rarely
occurs in the presence of a woody overstory . 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
Perennial snakeweed populations are often cyclic, dying back when
conditions for seedling establishment are unfavorable and then
reappearing when conditions are favorable . 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 .
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 . Germination occurs in early spring .
SPECIES: Gutierrezia microcephala
FIRE ECOLOGY OR ADAPTATIONS :
Desert shrub communities in which threadleaf snakeweed occurs do not
burn regularly. Fire frequency depends on the continuity of fuels,
which may only be adequate for fire after wet years. Fire in blackbrush
(Coleogyne ramosissima) communities is rare but does occur with high
temperatures, high wind velocity, and low relative humidity. Arid
grasslands burn more regularly than desert shrub communities. Where
livestock grazing has reduced grass cover, however, fire frequency has
decreased. Woody species have increased on grasslands with fire
suppression and heavy grazing [17,42].
Threadleaf snakeweed probably resists fire by regenerating from buried
seed and by surviving in unburned patches.
Find fire regime information for the plant communities in which this
species may occur by entering the species name in the FEIS home page
under "Find Fire Regimes".
POSTFIRE REGENERATION STRATEGY :
Ground residual colonizer (on-site, initial community)
Secondary colonizer - off-site seed
SPECIES: Gutierrezia microcephala
IMMEDIATE FIRE EFFECT ON PLANT :
Fire kills or severely damages perennial snakeweeds [15,20,42,43,44].
Threadleaf snakeweed probably burns readily because it is resinous.
DISCUSSION AND QUALIFICATION OF FIRE EFFECT :
PLANT RESPONSE TO FIRE :
Threadleaf snakeweed may colonize recently burned sites from buried seed
or seed from adjacent unburned sites if moisture conditions are
favorable and grass competition is not severe.
Although information pertaining to the response of threadleaf snakeweed
to fire is lacking in the literature, the presence of threadleaf
snakeweed on unburned and burned sites has been documented. In New
Mexico, threadleaf snakeweed had a density of 0.5 to 1.0 plant per
square meter on an arid grassland that had not experienced fire for at
least 30 years . Threadleaf snakeweed was present on some burn
sites but not others in blackbrush communities in southwestern Utah.
The vegetation was examined on eight sites, each having been burned once
in the past 37 years. Prefire species cover and frequency were not
known, and site histories differed. Threadleaf snakeweed was not
present on sites burned 1, 2, 6, and 37 years previously. It was
present on sites burned 12, 17, and 19.5 years previously, at absolute
covers of 0.3, 10.2, and 24.8 percent, respectively . The authors
did not discuss reasons for the variable presence of threadleaf
snakeweed. The 2-, 6-, and 12-year-old burns had been seeded with
grasses so colonization by threadleaf snakeweed may have been prevented
or delayed by grass competition.
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE :
FIRE MANAGEMENT CONSIDERATIONS :
Prescribed burning is frequently used as a management tool to increase
forage on rangelands . Historically, fire played an important role
in controlling woody species [20,42]. However, prescribed burning for
control of perennial snakeweeds has met with mixed success [24,42].
Wright and Bailey  suggested that fire can be used to control
perennial snakeweeds during wet weather cycles when the grasses will not
be severely damaged. The individual grass species and their ability to
recover from fire should be considered when prescribed burning for
perennial snakeweed control .
Prescribed burning of perennial snakeweeds is limited by inadequate fine
fuel. In a study of a broom snakeweed-infested grassland in southeastern
New Mexico, the area burned by spring prescribed fires did not exceed 60
percent unless the fine fuel loading exceeded 534 pounds per acre and
the litter fuel exceeded 1,000 pounds per acre, or the two fuels combined
exceeded 1,500 pounds per acre. If there is enough fuel, a headfire is
effective if the following criteria are met: litter moisture is 3 to
4.5 percent, fine fuel moisture is less than 20 percent, relative
humidity is less than 20 percent, ambient temperature is between 75 and
90 degrees Fahrenheit (24-32 deg C), and the wind speed is 8 to 15 miles
per hour .
SPECIES: Gutierrezia microcephala
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