Microsoft word - tribulus_terrestris_ucla_santamonicas.rtf

Tribulus terrestris L., PUNCTURE VINE. Annual, taprooted, several−many-stemmed at
base, matlike with radiating shoots often forked but not rooting at nodes, prostrate and
trailing, < 5 cm tall; shoots strongly 2-dimensional (plagiotropic) with suntracking leaves,
also closing upward in response to water stress, pubescent. Stems: cylindric, 2−3 mm in
diameter, sometimes zigzagged, commonly swollen at base and nodes, greenish soon
becoming brownish tan, tomentose and hispid. Leaves: opposite and alternate, even-1-
pinnately compound, pairs of lateral leaflets (2–)4–6(–7), petiolate, with stipules; stipules
2, fused to lower stem and petiole at swollen node, awl-shaped to narrowly triangular on
lower stem and lanceolate and crescent-shaped on upper side, (1–)1.5–5 mm long; petiole
4–7 mm long; rachis 10–30 mm long, 2-edged on upper side, tomentose and hispid;
petiolules < 1 mm long; blades of leaflets oblong or elliptic to lanceolate, 5–10 × 2–5 mm,
dull, ± asymmetric and oblique at base, entire, acute at tip, pinnately veined with midrib
conspicuous and raised on lower surface, upper surface with hairs only along midrib, lower
surface and margins sericeous, with irregular netlike of minor veins. Inflorescence:
flowers solitary, axillary (opposite leaf at node when leaves alternate), lacking bracts;
pedicel straight and slender, 4–9(–15) mm long. Flower: bisexual, radial, 6.5–10 mm
across, dish-shaped; receptacle a low, broad disc; sepals 5, spreading, unequal, lanceolate
to ovate, 3–4.2(–5) × 1.1–1.6 mm, green with membranous margins, acuminate or with
short point at tip, upper surface glabrous, lower surface hairy, deciduous; petals 5, ±
wedge-shaped, 2.5–4.7(–6) × 1.8–3.5 mm, bright yellow; nectaries 5, opposite sepals and
at bases of outer stamens, rectangular or sometimes weakly 2-lobed, ca. 0.2 × 0.3 mm long,
fleshy, green; stamens 10 in 2 whorls, free, attached to disc, unequal, sometimes the outer
whorl having shorter filaments and larger anthers; filaments 2–3(–4) mm long, yellow;
anthers versatile, dithecal, ± ellipsoid, 0.5–1.5 mm long, yellow, longitudinally dehiscent;
pollen yellow; pistil 1, subtended by low, broad disc; ovary superior, (4−)5-lobed, green,
lobes covered with erect, colorless bristles, lobes = chambers, each chamber with several
ovules attached to center; style ± club-shaped, ca. 1.5 mm long, green; stigmas = (4−)5
grooved ridges, radiating from and fused at tip of style, ca. 1.3 mm long, densely and
finely puberulent. Fruit: schizocarp, breaking into 4−5 dry, spiny mericarps (nutlets),
each mericarp 2–3(–5)-seeded, boney and indehiscent, straw-colored; intact fruit body
polygonal, ± 6−7 mm + 2(–4) spreading spines (prickles), with stout prickles on outer
corners, the prickles to 7 mm long and diverging 70−130°, exposed facets of original fruit
puberulent and with hard projections (from thick-based prickles) resembling short knobs
and horns; inner edge acute with the 2 converging facets glabrous and without spination or
other projections. Late May−mid-October.
Naturalized. Prostrate annual weed occurring in waste places, especially common during
summer along roadsides. Puncture vine was so named because the nasty, spiny fruits and
fruit segments easily puncture the skin, but also bicycle tires. Fruits of Tribulus terrestris
were the inspiration for a sharply pointed Roman weapon (caltrop) used to hobble cavalry
horses. Tribulus terrestris is one of several herbaceous species in range having
suntracking leaves; during daylight on sunny days its leaves are continuously oriented
more or less perpendicular to the sun’s rays, thereby maximizing photosynthesis. Tribulus
terrestris has radially symmetric, bright yellow flowers.
B. A. Prigge & A. C. Gibson

Source: http://www.smmflowers.org/bloom/PDF-species/Tribulus_terrestris_UCLA_SantaMonicas.pdf