1. Æsculus. Flowers irregular. Calyx 5-lobed. Petals 4 or 5. Stamens commonly 7. Fruit a leathery 3-valved pod. Leaves opposite, digitate.
2. Sapindus. Flowers regular. Sepals 4--5, in two rows. Petals 4--5. Stamens 8--10. Fruit a globose or 2--3-lobed berry. Leaves alternate, pinnate.
SUBORDER II. Acerineæ. (MAPLE FAMILY.) Flowers (polygamous or diœcious) small, regular, but usually unsymmetrical. Petals often wanting. Ovary 2-lobed and 2-celled, with a pair of ovules in each cell. Fruits winged, 1-seeded. Embryo coiled or folded; the cotyledons long and thin.--Leaves opposite, simple or compound.
3. Acer. Flowers polygamous. Leaves simple.
4. Negundo. Flowers diœcious. Leaves pinnate, with 3--5 leaflets.
SUBORDER III. Staphyleæ. (BLADDER-NUT FAMILY.) Flowers (perfect) regular; stamens as many as the petals. Ovules 1--8 in each cell. Seeds bony, with a straight embryo in scanty albumen.--Shrubs with opposite pinnately compound leaves, both stipulate and stipellate.
5. Staphylea. Lobes of the colored calyx and petals 5, erect. Stamens 5. Fruit a 3-celled bladdery-inflated pod.
Calyx tubular, 5-lobed, often oblique or gibbous at base. Petals 4--5, more or less unequal, with claws, nearly hypogynous. Stamens 7 (rarely 6 or 8); filaments long, slender, often unequal. Style 1; ovary 3-celled, with 2 ovules in each cell. Fruit a leathery pod, 3-celled and 3-seeded, or usually by abortion 1-celled and 1-seeded, loculicidally 3-valved. Seed very large, with thick shining coat, and a large round pale scar. Cotyledons very thick and fleshy, their contiguous faces coherent, remaining under ground in germination; plumule 2-leaved; radicle curved.--Trees or shrubs. Leaves opposite, digitate; leaflets serrate, straight-veined, like a Chestnut-leaf. Flowers in a terminal thyrse or dense panicle, often polygamous, most of them with imperfect pistils and sterile; pedicels jointed. Seeds farinaceous, but imbued with a bitter and narcotic principle. (The ancient name of some Oak or other mast-bearing tree.)
§ 1. ÆSCULUS proper. _Fruit covered with prickles when young._
Æ. HIPPOCÀSTANUM, L. (COMMON HORSE-CHESTNUT.) Corolla spreading, white spotted with purple and yellow, of 5 petals; stamens declined; leaflets 7.--Commonly planted. (Adv. from Asia via Eu.)