2. [Morus microphylla] Buckl. Mulberry. Mexican Mulberry.
Morus celtidifolia Sarg., not H. B. K.
Leaves ovate, acute or acuminate, rounded or rarely truncate, or often on vigorous shoots cordate at the broad base, and 3-lobed with shallow lateral sinuses and broad coarsely serrate lobes, when they unfold coated below with pale tomentum, and puberulous above, at maturity thin and firm in texture, dark green and often roughened on the upper surface by minute pale tubercles, and paler, smooth or scabrate, and glabrous or coated with soft pubescence on the lower surface, and often hirsute with short stiff pale hairs on the broad orange-colored midrib, and on the primary veins connected by conspicuous reticulate veinlets, rarely more than 1½′ long and ¾′ wide; turning yellow in the autumn; petioles slender, hoary-tomentose, becoming pubescent, ⅓′ in length; stipules linear-lanceolate, acute, sometimes falcate, white and scarious, coated with soft pale tomentum, about ½′ long. Flowers usually diœcious, staminate short-pedicellate, in short many-flowered spikes, ½′—¾′ long; calyx dark green, covered on the outer surface with soft pale hairs, deeply divided into equal rounded lobes reddish toward the apex; stamens with bright yellow anthers, their connectives conspicuous, dark green; pistillate sessile in few-flowered spikes, rarely ⅓′ in length; calyx divided to the base into thick rounded lobes, the 2 outer lobes much broader than the others, dark green, covered with pale scattered hairs; ovary green and glabrous, with short stigmatic lobes. Fruit: syncarp ½′ long, red becoming dark purple or nearly black, sweet and palatable; drupe ⅙′ long, ovoid, rounded at the ends, with a thin fleshy outer covering and a thick-walled light brown nutlet; seed ovoid, pointed, pale yellow.
A tree, sometimes 15°—20° high, with a trunk occasionally 12′—14′ in diameter, and slender branchlets covered when they first appear with soft white hairs, soon becoming glabrous or nearly so, and in their first winter light orange-red and marked by small lenticels and small horizontal nearly orbicular elevated concave leaf-scars displaying a ring of fibro-vascular bundle-scars; often a shrub. Winter-buds ovoid, acute, sharp-pointed, and covered by thin lustrous chestnut-brown ovate rounded scales scarious on the margins, those of the inner rows ovate-oblong, rounded at apex, pale-pubescent on the outer surface, and nearly 1′ long when fully grown. Bark smooth, sometimes nearly ½′ thick but usually thinner, light gray slightly tinged with red, deeply furrowed and broken on the surface into slightly appressed scales. Wood heavy, hard, close-grained, dark orange color or sometimes dark brown, with thick light-colored sapwood.
Distribution. Dry limestone hills, or westward only in elevated mountain cañons in the neighborhood of streams; valley of the Colorado River, Texas, southward into Mexico and through the mountain regions of western Texas and southern New Mexico to the Santa Rita Mountains and the cañons of the Colorado Plateau, Arizona.
2. MACLURA Nutt.
Toxylon (Ioxylon) Rafn.
A tree, with thick milky slightly acrid juice, thick deeply furrowed dark orange-colored bark, stout tough terete pale branchlets, with thick orange-colored pith, lengthening by an upper axillary bud, marked by pale orange-colored lenticels and armed with stout straight axillary spines, short stout spur-like lateral branchlets from buds at the base of the spines, and thick fleshy roots covered by bright orange-colored bark exfoliating freely in long thin persistent papery scales. Leaves involute in the bud, ovate to oblong-lanceolate, acuminate and apiculate at apex, rounded, cuneate or subcordate at base, entire, penniveined, the veins arcuate near the margins and connected by conspicuous reticulate veinlets; petioles elongated, slender, terete, pubescent; stipules lateral, nearly triangular, minute, hoary-tomentose, caducous. Flowers diœcious, light green, minute, appearing in early summer; calyx 4-lobed, the lobes imbricated in æstivation; the staminate long pedicellate, in short or ultimately elongated racemes borne on long slender drooping peduncles from the axils of crowded leaves on the spur-like branchlets of the previous year; calyx ovoid, gradually narrowed into the slender pubescent pedicel, coated on the outer surface with pale hairs, divided to the middle into equal acute boat-shaped lobes; stamens 4, inserted opposite the lobes of the calyx on the margins of the minute thin pulvinate disk; filaments flattened, light green, glabrous, infolded above the middle in the bud, with the anthers inverted and back to back, straightening abruptly in anthesis and becoming exserted; anthers oblong, attached on the back near the middle, introrse, 2-celled, the cells attached laterally to a minute oblong or semiorbicular connective, free and spreading above and below, opening by longitudinal lateral slits; pistillate sessile in dense globose many-flowered heads on short stout peduncles axillary on shoots of the year; calyx ovoid, divided to the base into oblong thick concave lobes, rounded, thickened, and covered with pale hairs at the apex, longer than the ovary and closely investing it, the 2 outer lobes much broader than the others, persistent and inclosing the fruit; ovary ovoid, compressed, sessile, green, and glabrous; style covered by elongated slender filiform white stigmatic hairs; ovule suspended from the apex of the cell, anatropous. Drupes oblong, compressed, rounded and often notched at apex, acute at base, with thin succulent flesh, and a thin crustaceous light brown nutlet, joined by the union of the thickened and much elongated perianths of the flowers into a globose compound fruit saturated with milky juice, mammillate on the surface by their thickened rounded summits, light yellow-green, usually of full size but seedless on isolated pistillate individuals. Seed oblong, compressed, rounded at base, oblique and marked at apex by the conspicuous oblong pale hilum, without albumen; seed-coat membranaceous, light chestnut-brown; embryo recurved; cotyledons oblong, nearly equal; radicle elongated, incumbent, ascending.
The genus is represented by a single species of eastern North America.