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).
[Illustration: FIGS. 471–473.--_Æsculus hippocastanum._
FIG. 471.--Diagram of the flower and of a scorpioid cyme.
FIG. 472.--Flower in longitudinal section.