Perennial, aquatic or swamp rhizomatous herbs, usually with milky juice. Leaves ensiform to orbicular. Flowers solitary or umbellate. Perianth 2-seriate, the outer 3 usually sepal-like, imbricate, the inner 3 petal-like and usually thin and deciduous. Stamens hypogynous, 8-9 or numerous; anthers basifixed, opening laterally. Carpels free; ovules numerous, scattered, on the reticulately branched parietal placentas. Fruits opening by the adaxial suture. Seeds numerous, without endosperm.
Notes: Distinguished from all other Monocotyledons by the peculiar placentation of the ovules, probably a primitive characteristic.
Perennial or annual, aquatic, swamp or marsh herbs, glabrous, usually lactiferous. Rhizome short; roots short, fibrous. Leaves erect or floating, basal; petiole with a sheathing base; leaf-blade entire, iridaceous, or lanceolate to orbicular with cuneate to truncate base and acute to rounded apex. Inflorescence umbellate, rarely with solitary flowers; bracts 2 or 3; bracteoles several; flowers regular, bisexual. Sepals 3, persistent. Petals 3, delicate. Stamens 6–9–?; filaments flattened; anthers 2-celled, dehiscing longitudinally and laterally. Carpels superior, free or joined at the base, 6–?, in a whorl, unilocular; style terminal; stigma sessile; ovules ?, scattered over the ovary-wall on a reticulate placenta. Fruiting carpels finally dehiscing along the ventral suture; seeds ?, smooth, wrinkled or ridged, rarely slightly spiny, without endosperm; embryo horseshoe-shaped or straight.A small family, confined to the tropics or subtropics except for Butomus L. which extends across Europe and Asia. The following genus is the only one which occurs in Africa.
Aquatic, freshwater, rhizomatous perennial. Rhizome dorsiventral, creeping, apparently monopodial, axillary buds sometimes developing into short-stalked bulbils. Leaves distichous or subdistichous, borne on the apex of the rhizome, erect, linear, glabrous not differentiated into petiole and blade, and up to 1m or more long, triquetrous, submerged or usually emergent, the base somewhat extended and sheathing below; intravaginal scales numerous. Scapes developed on alternate sides of the rhizome, usually separated by an odd number (5, 7, 9) offoliage leaves, erect, terete, glabrous. Inflorescence an umbel-like complex of cymes subtended by (2-)3(-4) bracts. Flowers pedicellate, perfect, protandrous, almost hypogynous, actinomorphic. Perianth of 6 petaloid tepals in 2 whorls, free, white to pink. Stamens 9, the outer whorl with 6 and the inner with 3; filaments flattened; anthers basifixed, 2-thecate, latrorsely and longitudinally dehiscent. Gynoecium of 6 conduplicate carpels arranged in 2 alternate whorls of 3, the carpels connate at the base into a ring, otherwise distinct, each apically narrowed into a crested ventral somewhat decurrent stigma; basally nectariferous on lateral carpel walls; placentation laminar. Ovules numerous, anatropous. Fruit of separate follicles, dehiscing by widening of the ventral sutures. Seeds numerous with ribbed testa and a straight embryo; endosperm lacking.
Only Butomus umbellatus L, widespread in temperate Eurasia and recently naturalised in eastern N America. Butomus junceus Turcz. is not considered to be worthy of specific status.
Butomus is found on the banks of still or slowly flowing water particularly in lakes, backwaters, ponds, ditches and canals. It is rarely found in swiftly flowing water, where it develops long, thin, pale green submerged leaves and does not flower. Triploids are more common in warm regions with alkaline and base-rich soils (Hroudova and Zakravsky 1993b); the diploids are commoner in cool, acid, base-poor substrata.
Butomaceae occur in most of Europe, but are absent from many islands (including the Azores, Iceland and many of the larger Mediterranean islands). The family extends eastwards to Manchuria with isolated populations in the Pamirs and eastern China. It has been introduced into N America, where it is spreading.
Butomus is commonly grown as an ornamental. In the rice fields of the Danube Delta it is considered an undesirable weed and in N America there is evidence that it is more competitive than many native reed-swamp species.
The rhizomes contain much starch and are eaten in parts of Russia; the starch is usually mixed with grain starch for making bread or the rhizomes may be prepared as a vegetable.
Little is known about seed dispersal. The seeds sink in water within a few minutes. Vegetative reproduction is efficient. Small rhizome fragments readily regenerate, axillary bulbils on the rhizome may also play an important role, and bulbils have been reported to develop in the inflorescence in plants from Scandinavia (Lohammer 1954). Under cultivation the species is usually propagated by division of the rhizome.
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