DIMORPHOCARPA Rollins, Publ. Bussey Inst. Harvard Univ. 1979: 20. 1979

Ihsan A. Al-Shehbaz

Tribe: Physarieae B. L. Robinson in A. Gray & S. Watson, Syn. Fl. N. Amer. 1(1): 100. 1895.

Name derivation: Latin dimorphos, two forms, and Greek karpos, fruit, in reference to the production in some species of two fruit types.

Type species: Dimorphocarpa wislizeni (Engelmann) Rollins (based on Dithyrea wislizenii Engelmann).

Herbs, annual, biennial, or perennial, densely pubescent throughout. Trichomes subsessile and stellate, mixed with minutely stalked dendritic, rarely simple. Multicellular glands absent. Stems erect or ascending, branched below and above. Basal leaves petiolate, not rosulate, simple, entire, dentate, or lobed; cauline leaves sessile or short-petiolate, not auriculate, simple, entire, dentate, or pinnatifid. Racemes many flowered, ebracteate, corymbose, elongated considerably in fruit; rachis straight; fruiting pedicels divaricate, sometimes ascending or slightly reflexed, persistent. Sepals oblong, free, caducous, widely spreading to reflexed, equal, base of lateral pair not saccate. Petals white to lavender, spreading, longer than sepals; blade obovate, obtuse; claw well differentiated from blade, shorter than sepals, glabrous, unappendaged, entire, often expanded at base. Stamens 6, somewhat spreading, tetradynamous; filaments wingless, unappendaged, glabrous, unappendaged; anthers oblong, not apiculate at apex. Nectar glands distinct, both lateral and median present. Ovules 2 per ovary, placentation apical. Fruits silicles, breaking up at maturity into 2 1-seeded units, didymous, strongly angustiseptate, not inflated, unsegmented; valves suborbicular or broader than long, thick papery, not veined, glabrous or pubescent, keeled, smooth, winged or wingless and margin indurated, enclosing seeds when falling off; gynophore to 0.5 mm; replum concealed by valve margin; septum complete, ca. 0.1 mm wide, not veined; style short or obsolete, persistent; stigma conical, decurrently 2-lobed though superficially appearing entire, unappendaged. Seeds aseriate, wingless, broadly oblong to suborbicular, strongly flattened; seed coat smooth, not mucilaginous when wetted; cotyledons accumbent to obliquely incumbent. x = 9.

Four species: N Mexico, SW United States.

References: Rollins (1958a, 1979).

                                           Key to the species of Dimorphocarpa

1. Fruit halves (7–)8–10 mm; petals (7–)8–10(–12) mm, claw not expanded at base;

  upper cauline leaves sessile....................................................................................................... 1. D. candicans

1. Fruit halves 3–5.5(–6.5) mm; petals (3.5–)4–7(–8) mm, claw expanded at base;

  upper cauline leaves short-petiolate, often cuneate at base.

      2. Perennials; fruit halves 3–4 mm wide; upper cauline leaves ovate to suborbicular,

          abruptly narrowed to petiole...................................................................................... 2. D. membranacea

      2. Annuals; fruit halves 5–7.5 mm wide; upper cauline leaves lanceolate to linear, cuneate at base.

      3. Upper cauline leaves pinnately lobed; fruit valves rounded at apex,

           about as long as wide............................................................................................. 3. D. pinnatifida

      3. Upper cauline leaves entire or rarely dentate; valves truncate at apex, often longer than 

          wide........................................................................................................................... 4. D. wislizeni