Celastrales Plant Order
qiazhan English name: Celastrales
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Celastrales, small order of flowering plants that includes 3 families, some 100 genera, and about 1,350 species. In the Angiosperm Phylogeny Group II (APG II) botanical classification system, Celastrales is placed in the Rosid I clade (see angiosperm).
Celastraceae
Celastraceae, or the bittersweet family, contains about 90 genera with some 1,300 species of trees, lianas, and herbs found throughout temperate and especially tropical regions. Maytenus (including Gymnosporia) contains about 200 species, Salacia about 150 species, and Hippocratea (including Loesneriella) about 120 species; all are pantropical. Euonymus (130 species) is more temperate, while Celastrus (32 species) is intermediate in its preferences.
Fresh leaves of Catha edulis (khat), a plant native in Africa and Arabia, yield a stimulant when chewed. It is especially popular in much of the Middle East. Species of Celastrus and Euonymus in particular are commonly cultivated as ornamental shrubs.
Many species in Celastraceae secrete gutta, or latex, and, if a leaf is pulled apart transversely, the two halves often hold together by thin strands of dried latex. The leaves can be spiral or opposite on a single plant, and in some species they are two-ranked. The leaf margins often have teeth, although these may be minute, and there are stipules that are quite often fringed. The flowers are usually small, with three or five stamens facing inward or outward and borne on the outside or inside of the prominent nectary disc. The ovary often has three compartments. The fruits and seeds are variable; the former may be fleshy or dry, and the latter may be winged, with a fleshy appendage or aril, or simply rounded.
Parnassiaceae
Parnassiaceae, with two genera, includes annual to perennial herbs. Parnassia contains 50 species that grow in the north temperate to Arctic region. Lepuropetalon spathulatum, the only species of its genus, occurs in the southeastern United States and Mexico. The leaves in the family have no stipules, and the flowers are single or obviously cymose. There are five stamens and five staminodes, or nonfunctional stamens. The latter are opposite the corolla, and at least sometimes nectar is secreted at their bases. The ovules are borne on the walls of the ovary, and the fruit is a capsule containing many small seeds. L. spathulatum is one of the smallest flowering plants growing on land. It is often less than 2 cm (1 inch) tall, and its flowers lack petals. The staminodes of Parnassia are branched, each branch ending in a shiny yellow knob; these appear to mimic nectaries.
Lepidobotryaceae
Lepidobotryaceae is a small family of two genera and two or three species of trees, Lepidobotrys staudtii being known from East Africa and Ruptiliocarpon caracolito growing in Central and South America. They have simple two-ranked leaves that are jointed at the base of the blade and have small paired leafy structures, or stipels, as well as ordinary stipules where the leaf joins the stem. The inflorescence seems to arise opposite the leaves. The flowers are small, male and female flowers being borne on different plants. The sepals and petals are free, and the 10 stamens are joined at their bases. The fruit wall has a layer with distinctive radial fibres that separate from a horny inner layer.
