Porter 1969, Kearney and Peebles 1961

Duration: Annual Nativity: Native Lifeform: Forb/Herb General: Herbaceous annuals, copiously and conspicuously pubescent; stems prostrate, 15- 70 cm long. Leaves: Opposite, pinnately compund, 1-4 cm long, 2-4 cm wide, with 3-4 pairs of leaflets; leaflets 12-19 mm long; stipules 3-6 mm long. Flowers: Yellow and solitary on peduncles from the leaf axils; peduncles shorter than subtending leaves, thickened distally, 5-12 mm long; sepals subulate, 2-4 mm long and 1 mm wide, hirsute and sparingly strigose, persistent, in fruit clasping mature mericarps and ca. 1/2 as long as them; petals 5, yellow, fading white to orange, obovate, 2-4 mm long and 1.5 mm wide. Fruits: Capsule broadly ovoid, the body 4-5 mm high, 6-8 mm wide, strigose, broadly tubercled; topped with a beak 1-4 mm long, shorter than the fruit body. Ecology: Found in riparian areas, desert grasslands and Chihuahuan scrub; in silty areas, mud flats, rocky areas, along streams and in woodlands and grasslands; below 5,500 ft (1676 m); flowers July-September. Distribution: s AZ, c and s NM, s TX to c MEX. Notes: Kallstroemia is a genus of prostrate, annual herbs with opposite, even-pinnate leaves, 5-petaled flowers on pedicels emerging from the leaf axils, and 10-lobed fruits that split into 10 reticulate nutlets at maturity. The style persists as a cap or beak on the top of the fruit until the fruit splits into nutlets. Sister genus Tribulus appears quite similar in growth form, but the fruits split into 5 spiny nutlets at maturity. K. hirsutissima is distinguished from Kallstroemias in the region by being copiously hairy with long spreading hairs, having small petals 2-4 mm long, fruits with beaks <4 mm long but stout and strongly cone-shaped with long hairs. It is most similar to K. california, another small-flowered species, and primarily differs from that species by being copiously hairy, having sepals that are persistent on the mature fruit, and nutlets with ridgelike tubercles. Ethnobotany: unknown Etymology: Kallstroemia is named for Anders Kallstrom (1733-1812) a contemporary of Giovanni Antonio Scopoli, the author of the genus, hirsutissima refers to the plant being copiously hairy. Synonyms: None Editor: FSCoburn 2014, AHazelton 2015