An Illustrated Guide to ARIZONA WEEDS
The University of Arizona Press
ORANGE CALTROP, Mexican poppy, summer poppy, Arizona poppy
ORANGE CALTROP-Kallstroemia grandiflora Torr.
DESCRIPTION-An erect, reclining, or prostrate annual, covered with long rough yellowish hairs, reproducing only by seeds. The stiffly hairy stems, branching from the base, are 1/2 to 2 or more feet long. The leaves are opposite, 1 1/4 to 3 inches long, and divided into 5 to 7 pairs of smooth margined hairy leaflets.
The large flowers have 5 deep orange petals 2/3 to 1 1/4 inches long. They are solitary on slender stalks, 1/2 to 2 inches long in the leaf axils. The greenish, somewhat pearshaped seedpods have cross ridges on the back, and are tipped by a long beak l/3 to 3/8 inch long. The pods split into 8 to 12 wedgeshaped, one-seeded nutlets at maturity. The nutlets are 3-angled, about 1/8 inch long, with 2 brownish and netted veined faces.
DISTRIBUTION-This beautiful native plant is common and very colorful on sandy or gravelly soil on mesas, slopes, washes, roadsides, and bottom lands in southern and central Arizona, from Greenlee to Yavapai to Yuma counties and southward; 100 to 5,000 feet elevation; flowering February to September, but mostly in July and August. It becomes troublesome when it volunteers in adjacent cotton and other crop fields in the irrigated valleys. In rich soil, as between cotton rows, the prostrate stems may be 4 feet long.
CALIFORNIA CALTROP-Kallstroemia californica (Wats.) Vail
DESCRIPTION-An annual very similar to orange caltrop, but the petals are only 1/4 inch. The seedpod beaks are no longer than 1/3 inch, and the backs of the seedpods have sharp tubercles. A native plant growing in the same type of places as orange caltrop, but found in northern as well as southern Arizona; 100 to 7,000 feet elevation; flowering May to October.
Copyright (c) 1972 The Arizona Board of Regents