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Family Lemnaceae

Synonyms: Lemnaceae APNI*

Description: Perennial herbs, mostly terrestrial or occasionally aquatic or climbers sometimes ± epiphytic; with underground or aerial stems or both; stem sympodial but usually appearing unbranched, sometimes monopodial with lateral branches; often with latex or acrid poisonous juice. Small aquatic herbs (re. former Lemnaceae taxa) can be floating on or near surface of the water, or completely submerged.

Leaves alternate, highly diverse; lamina [variously compound] or simple, [much lobed to] entire, hastate to linear, fine venation reticulate to parallel; petiole sheathing, rarely absent.

Small aquatic herbs (former Lemnaceae taxa) are solitary or in groups, each consisting of a ± globose or flat and leaf-like green plant body undifferentiated into stem and leaves (a thallus); roots absent or 1–several. Reproduction is usually vegetative by new leaf-like thalli emerging from a small slit or budding pouch; pouches usually 2, 1 on each margin or sometimes 1 marginal and the other on the upper surface; the young thalli remaining attached to the 'parent' thallus for some time.

Inflorescence terminal, or apparently lateral, solitary or clumped, a spadix subtended or partially enclosed by a spathe or rarely the spathe absent. Flowers small, bisexual, unisexual or sterile, if unisexual the plants monoecious and the sexes segregated in zones on the spadix, female lowermost, then sometimes a sterile zone, then male, then sometimes an uppermost sterile zone forming a variously shaped and often smelly appendix. Perianth absent or segments [9–] 6–4, free to fused. Stamens c. 4–10, free or fused; anthers 2- or 1-locular, dehiscing by pores or longitudinal [or transverse] slits. Ovary superior [to half-inferior], [from c. 50-] to a few- or 1-locular; ovules 1–many per loculus; style terminal and short or stigma sessile.

Small aquatic herbs (former Lemnaceae taxa) monoecious, with inflorescence of 1 female and 1 or 2 male flowers in 1 of the marginal pouches, or in the pouch on the upper surface. Flowers very rare, unisexual; perianth absent; male flowers with 1 or 2 stamens, anther 2- or 1-locular, dehiscing by longitudinal or transverse slits; female flowers with a 1-locular superior ovary, ovules 1–7, style short, unbranched.

Fruit fleshy; seeds 1–many, endosperm present or not in the mature seed. In small aquatic herbs (former Lemnaceae taxa) the fruit is a small 1–4-seeded utricle.


Distribution and occurrence: World: c. 123 genera, over 4000 species, cosmopolitan. Australia: c. 16 genera, c. 40 species (native and naturalised), all States.

External links:
Angiosperm Phylogeny Website (Family: Araceae, Order: Alismatales)
Wikipedia

The family includes plants of great economic importance, especially as staple tropical starch crops, including Colocasia esculenta (L.) Schott, Xanthosoma species, Cyrtosperma merkusii (Hassk.) Schott, Alocasia macrorrhizos (L.) Don and Amorphophallus paeoniifolius (Dennst.) Nicolson. Araceae, known generally as aroids, include numerous foliage houseplants forming the basis of a significant industry. Several have showy flowers, most notably species of Spathiphyllum, Zantedeschia and some Anthurium species. Some taxa have become major weeds.

Araceae includes small aquatic herbs that were formerly in the family Lemnaceae.

Text by Based on A. Hay, Araceae, in Flora of New South Wales Vol.4: 31-36 (1993) and B.J. Conn, Lemnaceae, in Flora of New South Wales Vol.4: 36-38 (1993); revised May 2017
Taxon concept: Australian Plant Census (accessed May 2017)

 Key to the genera 
1Roots absent and thallus more or less globose, ellipsoid or ovoidWolffia
Roots present and thallus more or less flattened (roots mostly absent in Lemna trisulca)2
2Roots 1 per thallus, rarely none; thallus with 1–5, often indistinct veinsLemna
Roots 1–18; thallus with 3–15, often indistinct veins
                       Back to 1
Spirodela

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