1911 Encyclopædia Britannica/Iridaceae

IRIDACEAE (the iris family), in botany, a natural order of flowering plants belonging to the series Liliiflorae of the class Monocotyledons, containing about 800 species in 57 genera, and widely distributed in temperate and tropical regions. The members of this order are generally perennial herbs growing from a corm as in Crocus and Gladiolus, or a rhizome as in Iris; more rarely, as in the Spanish iris, from a bulb. A few South African representatives have a shrubby habit. The flowers are hermaphrodite and regular as in Iris (fig. 1) and Crocus (fig. 3), or with a symmetry in the median plane as in Gladiolus. The petaloid perianth consists of two series, each with three members, which are joined below into a longer or shorter tube, followed by one whorl of three stamens; the inferior ovary is three-celled and contains numerous ovules on an axile placenta; the style is branched and the branches are often petaloid. The fruit (fig. 2) is a capsule opening between the partitions and containing generally a large number of roundish or angular seeds. The arrangement of the parts in the flower resembles that in the nearly allied order Amaryllidaceae (Narcissus, Snowdrop, &c.), but differs in the absence of the inner whorl of stamens.

Fig. 1.—Yellow Iris, Iris Pseudacorus.
1. Flower, from which the outer petals and the stigmas have been removed, leaving the inner petals (a) and stamens. 2. Pistil with petaloid stigmas.	3. Fruit cut across showing the three chambers containing seeds. 4. A seed. 1-4 about 1/2 nat. size.

Fig. 2.—Seed-vessel (capsule) of the Flower-de-Luce (iris), opening in a loculicidal manner. The three valves bear the septa in the centre and the opening takes place through the back of the chambers. Each valve is formed by the halves of contiguous carpels.

Fig. 3.—1. Crocus in flower, reduced. 2. Flower dissected. b, b′, Upper and lower membranous spathe-like bracts; c, Tube of perianth; d, Ovary;
e, Style; f, Stigmas.

The most important genera are Crocus (q.v.), with about 70 species, Iris (q.v.), with about 100, and Gladiolus (q.v.), with 150. Ixia, Freesia (q.v.) and Tritonia (including Montbretia), all natives of South Africa, are well known in cultivation. Sisyrinchium, blue-eyed grass, is a new-world genus extending from arctic America to Patagonia and the Falkland Isles. One species, S. angustifolium, an arctic and temperate North American species, is also native in Galway and Kerry in Ireland. Other British representatives of the order are: Iris Pseudacorus, (yellow iris), common by river-banks and ditches, I. foetidissima (stinking iris), Gladiolus communis, a rare plant found in the New Forest and the Isle of Wight, and Romulea Columnae, a small plant with narrow recurved leaves a few inches long and a short scape bearing one or more small regular funnel-shaped flowers, which occurs at Dawlish in Devonshire.