Iridaceae Juss.
  • Juss., Gen. Pl.: 57 (1789)


This taxon is accepted by WCS higher taxonomy

General Description

Perennial evergreen or deciduous herbs, occasionally shrubs with anomalous secondary growth (Klattia, Nivenia, Witsenia), rarely annuals (Sisyrinchium spp.), or an achlorophyllous saprophyte (Geosiris). Rootstock a rhizome, corm or bulb, or, when shrubs, a woody caudex or rootstock indistinct. Leaves basal and cauline, sometimes the lower 2-3 without blades, sheathing the stem base and reaching shortly above the ground (thus cataphylls), mostly distichous, the bases usually imbricate, sheaths of foliage leaves open or closed, usually contemporary with the flowers, occasionally produced later, rarely already dry at flowering, occasionally the leaves of the flowering stem with reduced to entirely sheathing blades, then foliage leaves sometimes produced from separate shoots; the blades either unifacial and oriented edgewise to the stem, parallel-veined, without or with a distinct central vein, this sometimes thickened, the surface plane, ribbed, plicate or occasionally terete, very rarely pseudopetiolate, narrow below and abruptly expanded above, or bifacial and oriented with the adaxial surface facing the stem, then channelled to flat and without a median vein; margins sometimes undulate to crisped, or thickened and fibrotic or raised into wings held at right angles to the surface; leaves achlorophyllous and scalelike in Geosiris. Flowering stems aerial or subterranean at anthesis, then emerging in fruit, simple or branched, terete or compressed, then often angled or winged, occasionally pubescent. Inflorescence either composed of I-many umbellate monochasial cymes (i.e. rhipidia) (Nivenioideae, Iridoideae) arranged in panicles or spikes or variously clustered terminally or on short lateral branches, the rhipidia paired and partly fused in Nivenioideae; rhipidia comprising pedicellate, occasionally subsessile, flowers each subtended by a single bract, enclosed, usually until anthesis, in large opposed sheathing bracts (spathes), the rhipidia occasionally solitary flowered; or a spike ofsessile flowers subtended by opposed bracts (Ixioideae), sometimes reduced to a single flower (e.g., Romulea, Xenoscapa), the inner (adaxial) bract forked apically and usually smaller, sometimes deeply divided, occasionally to the base (Babiana spp.). Flowers hermaphrodite, usually large and showy, with a petaloid perianth of 2 whorls of 3 tepals each, rarely the inner whorl suppressed, actinomorphic or zygomorphic (many Ixioideae), then usually bilabiate, the posterior tepal usually largest and inclined to hooded, the lower 3 often smallest, variously coloured, often with contrasting markings, when bilabiate the lower tepals marked with nectar guides; perianth of 6 petaloid tepals in 2 equal or more or less strongly different whorls, occasionally inner whorl reduced or lacking (especially Patersonia), tepals free to the base (most Iridodeae) or united in a tube (Nivenioideae, Ixioideae), the tube straight or curved, cylindric or funnel- to trumpet-shaped; nectaries septal (Ixioideae, Nivenioideae), perigonal (Iridoideae), on the base of the outer tepals (most Old World spp.) or the inner tepals (New World spp.) or nectaries lacking (e.g. most Aristea, Isophysis); oil glands (elaiophores) often present on the inner tepals on New World Iridoideae. Stamens 3 (2 in the Australian Diplarrhena), inserted at the base of the outer tepals, or in the tube, symmetrically disposed or unilateral and arcuate, or sometimes declinate; filaments filiform, free or partly to completely united, threadlike and not supporting the anthers in some New World genera; anthers basifixed to sub-basifixed or centrifixed, occasionally sagittate or versatile, 2-thecate, 4-sporangiate, extrorse to latrorse, opening by longitudinal slits, occasionally apically dehiscent. Gynoecium of 3 united carpels. Ovary inferior (but superior in the Tasmanian Isophysis) , 3-locular with axile placentation, rarely I-locular with parietal placentation (Hermodactylis); ovules anatropous or campylotropous, many to few, especially numerous and small in Geosiris, in 2 rows per locule, rarely in 1 row (Aristea); style terminal, filiform, usually 3-branched above, or 3-lobed, rarely simple (Zygotritonia), the style branches either filiform to distally expanded, sometimes each divided in the upper half, stigmatic towards the apices, or the branches thickened or flattened and petaloid, the stigmas then abaxial below the apices. Fruit a loculicidal capsule, rarely indehiscent, firm to cartilaginous, occasionally woody, xerochastic or rarely hygrochastic. Seeds often large, globose to angular or discoid, sometimes broadly winged, usually dry, brown, occasionally blackish, rarely the seed coat fleshy or an aril present, rugulose or smooth, shiny or mat; endosperm hard, with reserves of hemicellulose, oil and protein, rarely also starch; embryo small.

A family comprising ca. 70 genera and 1750 spp., cosmopolitan in distribution, but most abundant and diversified in southern Africa. More than 1/2 the species belonging to only 6 genera: Gladiolus (255), Iris (ca. 225), Moraea (200), Romulea (90), Geissorhiza (85), Crocus (80), and Sisyrinchium (ca. 80). These as well as Freesia (15), Ixia (45), Sparaxis (13), and Tigridia (ca. 30) are well known as ornamentals.

Ecology

Iridaceae are mostly small plants and thus often found in open scrub, desert or grassland. Members of the family also favour temperate climates and the distribution largely follows these conditions. Thus, species are concentrated in heathlands in S Africa and the Mediterranean (but poorly represented in similar vegetation types in Australia, Chile and western N America) and in the grasslands of cooler S America, the Andes or the higher elevation grasslands of Africa. Semideserts adjacent to these areas in temperate latitudes also have a fair representation of Iridaceae, notably the Middle East and Namaqualand and the Karoo in S Africa. Few Iridaceae grow in forest habitats but Neomarica stands out in the New World and Dietes in the Old. Several species of Iris also grow in forest, blooming early in the spring before the canopy closes. In Africa several species of Aristea, Crocosmia, Chasmanthe favour forest margins.

Distribution

Iridaceae have a nearly worldwide distribution but are especially well represented in S Africa and in temperate and highland S and Central America. Subfam. Ixioideae are largely African, and only Crocus exhibits radiation outside the continent, extending across Europe to the W Himalayas. Gladiolus and Romulea also occur in the Mediterranean and Middle East, but have their centre in the southern African winter-rainfall region. Several genera of Ixioideae occur in tropical Africa where Zygotritonia (4 spp.) and Savannosiphon (1) are endemic and Gladiolus has radiated significantly. Some 75 spp. of the genus are endemic to various centres across tropical sub-Saharan Africa. Most Ixioideae, however, are centred in the winter-rainfall area of South Africa, incl. the SW Cape, Namaqualand and the W Karoo (Babiana, Geissorhiza, Ixia, Sparaxis, Watsonia). Dierama is exceptional in being concentrated in eastern southern Africa, where there has been significant radiation in Gladiolus and Hesperantha as well. Notable disjunct geographical ranges include one sp. each of Babiana and Romulea on Socotra. The monotypic Isophysis is restricted to Tasmania. In subfam. Nivenioideae Aristea is widespread in Africa and Madagascar, where Geosiris is endemic. The shrubby genera Nivenia, Klattia and Witsenia are restricted to the SW Cape and only the Australasian Patersonia occurs outside Africa, extending through Australia to the mountains of New Guinea, Borneo and Sumatra. Subfamily Iridoideae comprises Irideae, largely Old World (incl. Australasia) excepting Iris, which also occurs in N America. Tribes Trimezieae and Tigrideae are exclusively New World, and Sisyrinchieae largely so. Sisyrinchium, largest genus of the Sisyrinchieae, extends throughout Sand N America including Greenland. Of the other genera of Sisyrinchieae, Solenomelus is restricted to the S Andes and Tapeinia to Patagonia, but Orthrosanthus extends north to Mexico as well as occurring throughout Australia. Libertia is found in Australia, New Guinea and New Zealand and in Andean S America. Olsynium has one sp. in western N America and the remainder occur in S America from Peru southward to Patagonia and one sp. is endemic on the Falkland Is. Iris, largest genus of Irideae is exclusive to the northern hemisphere and is unusual in Iridaceae in its development in centres like California, China, Europe and the Middle East. Four of the six spp. of Dietes are restricted to southern Africa, one more extends from S Africa to Kenya and Uganda, and one more occurs on Lord Howe Island (Australia). Moraea, the other large genus of Irideae, is widespread in subSaharan Africa and centred in the southern African winter-rainfall region. Moraea sect. Gynandriris has an unusual disjunction with two of the nine spp. native to the Mediterranean and Middle East. Tigrideae have radiated extensively in temperate S America where there are several small endemic genera (Gelasine, Kelissa, Onira) and in the Andes (Cardenanthus, Mastigostyla). A second New World centre is in northern Central America and Mexico, where Ainea, Cobana, Fosteria and Sessilanthera are endemic. Tigridia, the most speciose genus there, also occurs in Andean S America. Nemastylis is shared between the southern USA and Mexico and northern Mesoamerica. Cypella, one of the larger genera of Tigrideae, has a wide range in S and Central America including the West Indies. Herbertia has a notable disjunction with several spp. in Uruguay, S Brazil and Chile and one subsp. in southern USA.

Uses

Iridaceae are important in horticulture, both for the cut flower industry and for garden display. Gladiolus, Iris (mainly I. xiphium cultivars for the florist trade) and Freesia are the most important and are grown commercially especially in Europe and the USA. Several species and cultivars of Crocus, Freesia, Gladiolus, Iris and Watsonia are grown in gardens throughout the world and the trade in the corms, bulbs and rhizomes is considerable. Less well known in gardens are Belamcanda chinensis, Tigridia pavonia and species of Dietes, Ixia, Moraea, Sparaxis and Tritonia, but they are available in the nursery trade. The stigmas of Crocus sativus are the source of the spice saffron and the species is grown in parts of Europe, the Middle East and India for this spice. The corms of Crocus spp. are reported to be used as a food in Syria and corms of Lapeirousia are eaten today in parts of southern tropical Africa. Corms of many species were an important source of food for the early inhabitants of southern Africa. The corms of Moraea fugax are eaten today, but largely as a curiosity.

  Bibliography

  • 1 de Jussieu, A.L. Original publication of Iridaceae. (1789).
  • 2 Goldblatt, P., Manning, J.C. & Rudall, P.J. Iridaceae. Flowering Plants. Monocotyledons: Lilianae (excluding Orchidaceae) 295-333 (1998).

 Information From

WCS higher taxonomy
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