Flora of the Hawaiian Islands
Dicotyledon Literature for Tribulus terrestris
Wagner et al., 1990, 1999.
   Zygophyllaceae -- The Cresote Bush Family Bibliography
      Tribulus terrestris

Common name(s): caltrop, goat head, puncture vine
General Information
DistributionNative to the Mediterranean region, now widely naturalized in warm temperate and tropical regions.In the Hawaiian Islands, naturalized on Kaua`i, O`ahu, Moloka`i, Lana`i, Maui, Hawai`i.

Prostrate annual herbs; stems up to ca. 10 dm long.
Leaves 1-4.5 cm long, leaflets 3-6(-8) pairs, oblong to ovate or elliptic, 4-11 mm long, 2-4 mm wide, both surfaces moderately to densely sericeous to long-strigose, especially when young, stipules subulate, 2-5 mm long.
Peduncles densely antrorsely strigose and hirsute, the latter hair type with pustulate bases; sepals ovate to lanceolate, equal, 2-4.5 mm long, 1.5-2 mm wide, margins scarious; petals yellow, oblong to obovate, 3-5 mm long, 1-3 mm wide; outer nectaries yellowish(?), bilobed, inner whorl of nectary glands yellow(?), distinct; ovary long-strigose.
Fruit 5-12 mm in diameter, mericarps dorsally crested and tuberculate, bearing 2 stout hard spines 2.5-7 mm long, sometimes also with 2 smaller ones near base, the crests short-hirsute, the hairs with pustulate bases.
2n = 12, 24, 32, 36, 48