Hiraea sect. Pachyantaeris Griseb., Linnaea 13: 244. 1839.—Lectotype, designated by C. V. Morton, 1968: H. platyptera Griseb. [C. psilophyllum (Adr. Juss.) D. M. Johnson].
Mascagnia subg. Plagiogynixa Nied., Arbeiten Bot. Inst. Königl. Lyceum Hosianum Braunsberg 3: 27. 1908.—Lectotype, designated by D. M. Johnson, 1986: M. macroptera (DC.) Nied. [C. macropterum (DC.) D. M. Johnson].Cabi Ducke, Arq. Serv. Florest. 2: 13. 1943.—Type: Cabi paraensis Ducke [Callaeum antifebrile (Griseb.) D. M. Johnson].
Woody vines, or shrubs with scandent or trailing branches; stipules very small, borne on petiole at or just above base (somewhat below to beyond middle of petiole in C. johnsonii), occasionally absent; petiole eglandular or biglandular near or beyond middle; lamina bearing small glands at or on margin in proximal half, occasionally eglandular. Inflorescences axillary or terminal, simple or compound, with the flowers in few-flowered umbels or corymbs or in short, mostly decussate pseudoracemes; floriferous bracts eglandular; floriferous peduncle developed, short to long; bracteoles eglandular, borne at or (often) below apex of peduncle. Sepals leaving petals exposed during enlargement of bud, appressed or recurved at apex in anthesis, the lateral 4 bearing large paired abaxial glands, the anterior eglandular; corolla bilaterally symmetrical, the posterior petal with its claw thicker and longer than in lateral petals and its limb usually smaller; petals lemon-yellow, glabrous or abaxially sericeous or tomentose; androecium bilaterally symmetrical; stamens all fertile or the posterior 3 occasionally sterile, glabrous; filaments 1/3–2/3 or more connate, straight; anterior 7 anthers ± alike, usually larger than the posterior 3 (those opposite posterior petal and adjacent sepals); gynoecium bilaterally symmetrical; ovary with the carpels completely connate; styles 3, erect or divergent from base, nearly straight or slightly sigmoid, subequal, with the apex dorsally rounded and the stigma internal and transversely expanded. Samaras separating from a pyramidal torus; samara (excepting the nutlike mericarp of C. antifebrile with vestigial wings) butterfly-shaped to depressed-elliptical, the lateral wings chartaceous with many fine parallel veins, cleft to nut at apex, continuous at base or cleft part-way or completely to nut, the margin entire, undulate, or coarsely toothed; dorsal wing distinct at apex and base or connate with lateral wings at base, varying from small to nearly as large as lateral wings, a few species with ruffles or winglets between dorsal and lateral wings; base of wings thickened with spongy tissue; ventral areole ovate to linear. Chromosome number: n = 10 (C. macropterum and C. septentrionale; W. R. Anderson, 1993a); photo.
Eleven species of western Texas, Mexico, Central America, and South America. In Mexico and Central America it is found most often in seasonally dry woodlands, thickets, or more open places; the South American species are more likely to grow in mesic or wet habitats. It seems likely that the populations of C. antifebrile (Griseb.) D. M. Johnson in Falcón, Venezuela, and near the mouth of the Amazon resulted from cultivation of a species that is otherwise native in westernmost Amazonia; see Johnson, 1986 [pdf], and below under Uses. [map] — Regional key to genera: USA, Central America.
Callaeum is distinguished among the genera of this clade by having the posterior three anthers smaller than the other seven, by the transversely expanded stigmas, and by the combination of epipetiolar stipules, marginal leaf glands, and yellow petals exposed in the enlarging bud. Six of the eleven species (C. antifebrile, C. clavipetalum, C. malpighioides, C. nicaraguense, C. psilophyllum, and C. septentrionale) are included in the latest sampling of DNA sequences (Davis & Anderson, 2010 [pdf]), and the bootstrap support for the genus is 100%. For notes on reduced fruits like those found in C. antifebrile, see the discussion of Malpighiodes.
In his revision of Callaeum (1986), D. M. Johnson cited a specimen of C. macropterum (DC.) D. M. Johnson, Palmer s.n. in 1869 (NY), as coming from Arizona, "without definite locality." That species occurs in Sonora fairly close to the U.S. border, but no other collection is known from north of the border. In his 1956 book on Edward Palmer, Rogers McVaugh said that in 1869 Palmer collected in Arizona but was in southernmost Arizona only a short time; from Tucson he took a coach south into Sonora, Mexico, where he collected in several areas, including the Yaqui River (pp. 43–44). NY has two sheets of C. macropterum labeled as Palmer s.n. in 1869, one with a label giving the locality as "Arizona," the other with a label giving the locality as "Yaqui River Sonora." The specimens look as if they were parts of the same gathering. Given McVaugh's cautionary notes on the inaccuracies found in many of the labels placed on Palmer's collections after his return to Washington (see p. 131), it seems likely that the specimen cited by Johnson as coming from Arizona actually originated on the Yaqui River in Sonora. The species C. septentrionale (Adr. Juss.) D. M. Johnson does occur in the United States; it is known from one specimen collected near Laredo, Texas, just across the border from its northernmost occurrence in Mexico.
Etymology: The name Callaeum comes from the Greek word for cockscomb (kallaion), referring to the lobed or corrugated outgrowths found on the samara between the lateral and dorsal wings in the type species, C. nicaraguense (Griseb.) Small.
Uses: Callaeum antifebrile is reported to have hallucinogenic properties and to be useful as a febrifuge, and its leaves and stem are used in the treatment of internal and external sores; see Johnson, 1986. Both C. macropterum and C. septentrionale are cultivated as ornamentals in Arizona and California (T. F. Daniel and S. G. Weller, pers. comm.).