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Published In: Species Plantarum 1: 195. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 9/8/2017)
Acceptance : Accepted

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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.

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