2. Ceanothus
L.
Plants small
shrubs (larger and rarely treelike elsewhere). Stems branched, not twining,
brittle or flexible, green to brown, sometimes developing longitudinal fissures
with age, the branches not spine-tipped. Twigs green to brown or light
yellowish brown, glabrous to densely and minutely hairy. Leaves alternate,
mostly short-petiolate. Leaf blades variously shaped, the margins sharply and
finely toothed, the teeth gland-tipped when young, the surfaces glabrous to
densely short-hairy, not shiny, the venation with 3 main veins that diverge at
or just above the blade base and are connected by numerous, pinnate finer
veins. Inflorescences terminal on present year’s growth, either on the main
branchlets or at the tips of short axillary branches, of relatively dense,
small panicles, the branches often somewhat umbellate, occasionally reduced to
umbels. Flowers perfect, with relatively long, slender stalks. Hypanthium
small, 3–4 mm in diameter at fruiting. Sepals 5, oblong, somewhat concave and
the tips incurved at flowering. Petals 5, tapered to long stalked bases, white.
Stamens 5, exserted. Ovary 3-locular, shallowly 3-lobed at the tip, the style
3-branched toward the tip. Fruits capsulelike, modified drupes, 4–6 mm long,
depressed-obovoid, with usually 3 stones, the outer surface thin, leathery,
black, not glaucous, the stones dehiscing explosively at maturity, tearing open
the outer fruit layers and expelling the seeds. Seeds 1.5–2.0 mm long, more or
less obovate in outline, somewhat anglar, the surface smooth, reddish brown to
brown, shiny. About 60 species, North America, Central America, most diverse in
the western U.S.
Nearly 45
species of Ceanothus occur in California, where some of them are
conspicuous elements of chaparral and woodland plant communities. These shrubs
flower profusely in the spring with showy displays of fragrant, white to purple
flowers. They are appreciated in their natural environments and also prized in
cultivation as ornamental shrubs. Further, it has been known for some time that
some species in the genus (including C. americanus) produce root nodules
(Furman, 1959) similar to those found in many Fabaceae. These nodules contain
symbiotic, nitrogen-fixing bacteria capable of converting atmospheric nitrogen
into ntirates to improve soil fertility (Bond, 1967). The two Missouri species
are western-occurring components of a small group of only four or five species
that occur natively east of the Mississippi River. They were among the first
members of the genus to be brought into cultivation, with many cultivars
produced, but seem to have fallen from favor during the first half of the
twentieth century. In recent years, they have had a revival of sorts and have
become increasingly available again as ornamentals, especially through
wildflower nurseries. The leaves of the Missouri species were used by Native
Americans in a tea and the often extensive, woody rootstocks were used for
fuelwood in areas where aboveground biomass of other woody species was low
(Kurz, 1997; Moerman, 1998). Medicinally they have been used as a coagulant and
historically were an ineffective treatment for syphilis.
The fruits of Ceanothus
have sometimes been described as capsules, but technically they are modified
drupes (Brizicky, 1964a). The somewhat fleshy fruits contain usually three
stones. At maturity, these split open explosively, tearing open the outer fruit
layers and expelling the seeds. The remainder of the fruit is shed at that time
or soon thereafter, leaving the persistent hypanthia.