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Iridaceae in sub-Saharan Africa
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Published In: Genera Plantarum 57. 1789. (4 Aug 1789) (Gen. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 6/6/2016)
Taxon Profile     (Last Modified On 2/5/2017)
Description: Perennial evergreen or deciduous herbs, rarely annuals or shrubs with anomalous secondary growth. Rootstock a rhizome, bulb, corm, or when shrubs, a woody caudex. Leaves basal and cauline, sometimes lower 2 or 3 without blades, sheathing stem base and reaching shortly above ground (thus cataphylls); mostly in two opposed ranks, bases usually overlapping and clasping the one above, sheaths of foliage leaves open or closed, usually contemporary with flowers, occasionally produced later, rarely already dry at flowering, occasionally leaves of flowering stem with reduced to entirely sheathing blades, then foliage leaves sometimes produced from separate shoots; blades either unifacial and oriented edgewise to stem, parallel-veined, without or with a distinct central vein, surface plane or pleated or occasionally oval to round in section; or bifacial and oriented with adaxial surface facing stem, then channelled to flat and usually without a median vein; margins plane or sometimes undulate to crisped, sometimes thickened and fibrotic or raised into wings held above surface. Flowering stems aerial or subterranean, simple or branched, round in section or compressed, then often angled or winged. Inflorescence either composed of umbellate monochasial cymes (rhipidia) enclosed in opposed leafy to dry bracts (spathes) with flowers usually pedicellate, sometimes sessile, each flower within a rhipidium subtended by one bract; or flowers sessile, subtended by a pair of opposed bracts and arranged in a spike, or solitary. Flowers bisexual, with a petaloid perianth of 2 whorls of 3 tepals each, rarely inner whorl reduced or lacking, radially or bilaterally symmetric, then usually bilabiate, variously coloured, often with contrasting markings; scented or unscented; tepals usually large and showy, free or united below in a tube, whorls equal or unequal, when zygomorphic posterior tepal usually largest and inclined to hooded, lower 3 often smallest and with contrasting markings (nectar guides); tube when present straight or curved, cylindric or funnel- to trumpet-shaped. Stamens 3 (2 in Australian Diplarrena), arising at base of outer tepals, or within floral tube, symmetrically disposed or unilateral and arcuate or sometimes declinate; filaments filiform, free or partly to completely united; anthers 2-thecous, usually extrorse and splitting longitudinally, occasionally splitting laterally or at apex or base. Ovary inferior (but superior in Australian Isophysis), 3-locular with axile placentation (rarely 1-locular with parietal placentation); ovules anatropous or campylotropous, many to few, in 2 rows (rarely 1 row) per locule; style filiform, 3-branched or 3-lobed, style branches either filiform (sometimes very short) to distally expanded, sometimes each divided in upper half and stigmatic towards apices, or branches thickened or flattened and petaloid, stigmas then abaxial below apices. Fruit a loculicidal capsule, rarely indehiscent, firm to cartilaginous, occasionally woody, xerochastic or rarely hygrochastic. Seeds globose to angular or discoid, sometimes broadly winged, usually dry, rarely seed coat fleshy or an aril present, rugulose or smooth, shiny or matte; endosperm hard, with reserves of hemicellulose, oil and protein; embryo small. Pollen grains monosulcate, trisulcate, zonasulculate, dizonasulculate, spiraperturate or inaperturate, operculate or not, exine reticulate to areolate, micropunctate, or perforate-scabrate.
General Notes:

With an almost worldwide distribution, the family Iridaceae comprises some 2250 to 2300 species divided among six subfamilies. Southern Africa, that is the subcontinent south of the Cunene--Limpopo axis, is a major centre for the family and accounts for some 1210 species, thus slightly more than half the total species. Almost all species and most genera are restricted to southern Africa, and just a few are shared with adjacent tropical Africa and Madagascar. Crocoideae, the largest subfamily, is centred in southern Africa and largely in the winter-rainfall southwest and comprises 28 genera, two of which are shared with western Eurasia and one, Crocus, occurs only in north Africa and Eurasia. Iridoideae, with 225 species in southern Africa, also occurs in Eurasia and the Americas, and includes the Eurasian and North American genus Iris and the large African genus Moraea. Aristeoideae, with only one genus, Aristea, is likewise centred in southern Africa; several species are shared with tropical Africa, and several more occur in Madagascar. Lastly, subfamily Nivenioideae with just three genera and 15 species occurs exclusively in the Cape Region of South Africa and includes the shrubby members of the family, representing a remarkable growth form for Iridaceae and for the monocots. All Crocoideae and most Iridoideae are seasonal geophytes with underground storage organs formed from modified stems called corms. Those of Crocoideae are very different in anatomical structure and ontogeny from those of southern African Iridoideae and arose independently. Dietes and Bobartia of the Iridoideae and some Aristea species are evergreen, rhizomatous plants as are a few species of Watsonia and Tritoniopsis in Crocoideae, the remaining species being deciduous, thus surviving underground in the dry season. In contrast, species of Nivenioideae are woody, evergrren shrubs with multiple branches produced from a woody, underground caudex. Leaves of most Iridaceae are Iris-like, thus are unifacial and isobilateral and are oriented in a single plane with the blades usually upright. The leaf margins sometimes show surprising development as in thickened margins, sometimes raised into broad wings or the midveins may be hugely raised rendering the leaf cross shaped in section. In Crocus, Moraea and Syringodea the leaves are secondarily bifacial, thus appearing to correspond to the typical condition in plants. Flowers of Iridaceae are their most striking feature, and are very variable in shape, size, and colour and are adapted for a wide range of insect and bird pollinators, including pollen collecting female bees, large-bodied, long-tongued apid and anthophorine bees, long-proboscid flies, short-proboscid dung, game and muscid flies, both settling and hovering sphinx moth, butterflies to name the most important. Some species of Sisyrinchium L. are reported to be naturalized locally in South Africa.


 

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1 Plants evergreen shrubs with woody aerial stems; rootstock a woody caudex; individual flowers sessile and the tepals always united in a well-developed tube and lasting at least two days Nivenioideae
+ Plants perennial, either with aerial stems not woody or acaulescent, sometimes evergreen; rootstock a rhizome or corm; individual flowers stalked or sessile, the tepals free, basally connate, or united in a tube; lasting < 1 day and deliquescing on fading (2)
2 (1) Flowers in umbellate clusters (rhipidia) enclosed by a pair of opposed leafy bracts (spathes), rarely solitary on the peduncles or plants acaulescent but then style either dividing below the anthers into tangentially compressed, petal-like branches or dividing below or above the base of the anthers and obscurely 3-lobed apically, the lobes entire or fringed, individual flowers pedicellate, sometimes sessile; rootstock a rhizome, a corm rooting from the apical bud; flowers with the tepals free to basally connate, or united in an extended tube; lasting a single day or 2 or more days; nectaries septal or perigonal or oil glands present (3)
+ Flowers sessile and subtended by a pair of opposed bracts, usually arranged in a spike or solitary on branches; tepals always united in a tube below; flowers lasting at least 2 days; style dividing into filiform branches, rarely simple; rootstock a corm producing roots from the base; pollen grains usually with perforate scabrate exine, rarely exine reticulate; monosulcate, apertures usually with operculum unless zonosulcate; nectaries septal Crocoideae
3 (2) Rhipidia (flowers clusters), or at least the terminal, united in pairs (binate); style notched or divided apically into 3 lobes, occasionally forming filiform branches; nectaries rarely present, then perigonal Aristeoideae
+ Rhipidia (flowers clusters) never united in pairs; style dividing below level of anthers into 3 branches, these either filiform, extending between the stamens or thickened or flattened and lying opposite stamens, usually each terminating in paired appendages (style crests); nectaries or oil glands when present perigonal Iridoideae
 

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