The essential characters of this family are in the main the same as those of the Terebinthinæ and Gruinales. The flowers are hypogynous, perfect, with free petals, 5-merous (S5, P5, typically A5 + 5, all of which, however, are not generally developed; in our native orders there are only 7–8 stamens), and most frequently a 3-merous, 3-locular gynœceum (less frequently 2 or 5 carpels with as many loculi). In each loculus there are usually only 1–2 ovules. A deviation from the preceding families is the frequent zygomorphy of the flower, with, as a rule an oblique plane of symmetry (Fig. [471]). When a disc is developed it is placed outside the stamens. The majority have no endosperm (Fig. [473]).—The members of the family are nearly all trees.
The family is closely allied to the Terebinthinæ, but unlike this it never has aromatic properties, and differs also in the position of the nectary, in the flowers, which are often irregular with a reduction in the number of stamens, and in the ovule which is usually ascending with micropyle pointing downwards (the Terebinthinæ having the micropyle turned upwards), etc. It is also related to Frangulinæ, the Staphyleaceæ being the chief connecting link; but the Æsculinæ generally have compound leaves.
Order 1. Staphyleaceæ. Leaves opposite, often compound. Flowers regular, ☿, 5-merous in calyx and corolla, 5-stamened. The stamens are placed outside the nectary. Ovary syncarpous or 2–3-partite with free styles. The capsule is thin, bladder-like, 2–3-locular, opening at the apex, and has several very hard seeds with a shining testa without aril. Endosperm. Staphylea pinnata (S. Europe) and trifoliata (N. Am.) are cultivated in gardens; they have white flowers in pendulous, axillary racemes or panicles.—16 species.—Staphylea is found in the Tertiary of N. America.
Order 2. Melianthaceæ. Glaucous shrubs with scattered, pinnate leaves, and large stipules. Melianthus.—8 species; S. Africa.
Order 3. Sapindaceæ. Trees or shrubs, often climbing by tendrils (lianes with anomalous structure of the stem) and with compound leaves. The flowers, in most cases, are small, insignificant, and without scent, and in some polygamous and zygomorphic. S4–5, P4–5, A8 (less frequently 5–10) inside the nectary (disc); ovary generally 3-locular, with 1–2 ovules in each loculus (raphe ventral, micropyle turned downwards). Seed without endosperm, often with an aril. The embryo is often thick and curved (Fig. [473]).
Figs. 471–473.—Æsculus hippocastanum.
Fig. 471.—Diagram of the flower and of a scorpioid cyme.
Fig. 472.—Flower in longitudinal section.