Leaves trifoliate with tomentose or nearly glabrous rachis and petiolules; leaflets oblong-ovate to rhombic, acuminate and long-pointed at apex, cuneate or unsymmetrically rounded at base, coarsely serrate above the middle, or nearly entire, when they unfold hoary-tomentose below and densely pubescent above, occasionally deeply lobed, glabrous on the upper surface except along the midrib and veins, thickly coated on the lower surface with matted pale hairs and furnished with large axillary tufts. Fruit on pubescent pedicels, puberulous or nearly glabrous, not constricted or rarely slightly constricted at base.
A tree, 20°—50° high, with dark bark, hoary-tomentose branchlets and winter-buds.
Distribution. California, valley of the lower Sacramento River and the interior valleys of the coast ranges from the Bay of San Francisco to Santa Barbara County and in elevated cañons on the western slopes of the San Bernardino Mountains; widely distributed but nowhere abundant.
Occasionally planted in California.
XXXVI. HIPPOCASTANACEÆ.
Trees or rarely shrubs, with stout terete branchlets conspicuously marked by triangular leaf-scars, fetid bark, thick fleshy roots, and large scaly winter-buds, the inner scales accrescent with the young shoots and often brightly colored. Leaves opposite, digitately compound, without stipules, deciduous; leaflets 3—9, lanceolate or ovate, serrate, pinnately veined. Flowers polygamo-monœcious, showy, white, red, or pale yellow, on stout jointed pedicels from the axils of minute caducous bracts, racemose or nearly unilateral on the branches of large terminal thyrsi or panicles, appearing later than the leaves, only those near the base of the branches of the inflorescence perfect and fertile; calyx 5 or rarely 2-lobed, the lobes imbricated in the bud, unequal, campanulate or tubular, the lobes imbricated in the bud, mostly oblique or posteriorly gibbous at base; disk hypogynous, annular, depressed, lobed, more or less gibbous posteriorly; petals 4 or 5, imbricated in the bud, alternate with the lobes of the calyx, deciduous, the anterior petal often abortive, unguiculate, the margins of the claw commonly involute; stamens 6—8, rarely 5, generally 7, inserted on the disk, free, unequal; filaments filiform; anthers ellipsoid, glandular-apiculate, attached on the back below the middle, introrse, 2-celled, the contiguous cells opening longitudinally; ovary sessile, oblong or lanceolate, 3-celled, echinate or glabrous, rudimentary in the staminate flower; style slender, elongated, generally more or less curved; stigma terminal, entire, mostly acute; ovules 2 in each cell, borne on the middle of its inner angle, amphitropous, the upper ascending, the micropyle inferior, the lower pendulous, the micropyle superior. Fruit an echinate or smooth coriaceous capsule, 3-celled and loculicidally 3-valved, the cells 1-seeded by abortion, often by suppression 1 or 2-celled, and then 1 or 2-seeded, the remnants of the abortive cells and seeds commonly visible at its maturity. Seeds without albumen, round when one is developed, or, when more than one, flattened by mutual pressure; seed-coat coriaceous, dark chestnut-brown or pale orange-brown, smooth and lustrous, with a broad opaque light-colored hilum; embryo filling the cavity of the seed; cotyledons very thick and fleshy, often conferruminate, unequal, incurved on the short conic radicle, remaining under ground in germination; plumule conspicuously 2-leaved.
The Horsechestnut family is composed of the widely distributed genus Aesculus and of Billia Peyr., a genus of two species of Mexican and Central American trees, differing from Aesculus in its 3-foliolate leaves.
1. AESCULUS L.
Characters of the family; leaves 5—9-foliolate.
Aesculus with fifteen or sixteen species, is represented in the floras of the three continents of the northern hemisphere and is most abundant in the southeastern United States. It produces soft straight-grained light-colored wood and bitter and astringent bark. The seeds contain a bitter principle, aesculin. Aesculus Hippocastanum L., of the mountains of Greece, the common Horsechestnut of gardens, is largely planted as an ornamental tree in all countries with temperate climates, and now occasionally grows spontaneously in the eastern states.