[Ulex europaeus L.][ULEEU][CalEPPC: A-1][CDFA list:
B] Photographs Map
of Distribution Biocontrol
prickly or thorn broom, furze, whin
DESCRIPTION: Spiny evergreen shrub with yellow pea-like
flowers, to 3.5 m tall. Gorse typically forms dense
impenetrable thickets that exclude desirable vegetation and increase
fire hazard risks. Mature plants contain ~2-4 % flammable oils.
Older shrubs develop a central mass of dead material and are particularly
flammable. Abundant leaf litter acidifies upper soil layers. Introduced
from Western Europe as an ornamental or hedge shrub. The gorse
seed weevil (Apion ulicis) and spider mite (Tetranychus
lintearius) are introduced biocontrol agents currently established
in California. The seed weevil reduces seed production, but cannot
kill established stands. Heavy mite infestations can kill branches
and are apparent by the dense webbing that covers the foliage.
sessile, oblong, 5-7 mm long, bases slightly tapered, tip rounded,
leathery, glabrous. Stalk below cotyledons (hypocotyl) +/- woody,
glabrous. First leaves mostly simple, alternate, sessile, +/-
lanceolate, 2-5 mm long, tips acute, leathery, covered with stiff
unicellular hairs. Subsequent leaves usually compound with (2-)3
leaflets, ~ 5-10 mm long, otherwise similar to first leaves. Juvenile
plants typically lack lateral branches and have compound leaves
with 3 leaflets.
Stems highly branched, interwoven, stiff, spreading, longitudinally
ridged. New stems green, covered with hairs. Branchlets terminate
as thorns. Leaves alternate. Unlike juveniles, mature
shrubs have simple leaves modified into stiff,
curved awl-like spines, 5-30 mm long. Stipules lacking.
and UNDERGROUND STRUCTURES: Taproot typically poorly developed. Lateral roots
extensive, branched, mostly shallow, but a few penetrate the soil
more deeply. Lower branches resting on soil may develop adventitious
roots at the base. Roots associated with nitrogen-fixing bacteria.
Flowers axillary, solitary or in few-flowered clusters. Petals
yellow, 15-20 mm long, persistent. Calyx (sepals as a unit)
yellow, membranous, deeply 2-lipped, 10-15 mm long,
upper lip 2-toothed, lower lip 3-toothed, covered with short hairs.
Stamen filaments fused into a tube.
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and SEEDS: Pods ovoid to oblong, 1-2 cm long, slightly
flattened, dark brown, covered with tawny spreading wavy hairs,
partially enclosed by the calyx. Seeds 2-6, shiny green to brown,
smooth, +/- triangular, flattened, ~ 3 mm long, with a straw-colored
sites, sand dunes, fields, pastures, logged areas, burned sites,
particularly where winters are mild and some moisture is available
year round. Frost-damaged plants can resprout from the crown.
Does not survive severe cold winter or arid climates. Grows best
on acidic (pH 4.5-5.0) soil. Tolerates most soil types, including
serpentine, but seldom grows in high calcium (calcareous) soils.
DISTRIBUTION: North Coast,
western North Coast Ranges, northern and central Sierra Nevada
foothills, San Francisco Bay region, eastern South Coast Ranges,
South Coast, Peninsular Ranges; to Washington. To 400 m (1300
by seed. Plants produce abundant quantities of seed. Most
seeds are ejected to within 5 m of the parent shrub when pods
snap open at maturity. Some seeds may disperse to greater distances
with human activities, water, soil movement, animals, and ants.
Seeds are hard-coated and can survive for more than 30 years under
field conditions. Large soil seed banks often accumulate. Scarification
or heating often stimulates germination. Optimal temperature for
germination is between 15-19º C. Germination can occur year
round when conditions are favorable. Shrubs may live for up to
~ 30 years.
FAVORING/DISCOURAGING SURVIVAL: Plants cut or burned to ground level may resprout
from the crown. Burning often stimulates a flush of seedling germination
after the first rain. Browsing and trampling by goats can greatly
reduce seedling establishment and crown re-growth.
Unlike gorse, the brooms (Cytisus, Genista, Spartium,
Retama species) lack spiny foliage.
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