On-Line Key to the Genus Spirodela
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Spirodela & Landoltia 1

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Plant body flattened, oval-orbicular in outline with 3-12 (15) veins, 4-10 mm long, dark lustrous green above and reddish-purple beneath; floating solitary or remaining attached in clusters of 2-5; dorsal surface often with row of papules along midline; membranous, scalelike prophyllum enveloping dorsal and ventral surface of basal end, visible only on young plants and turions of S. polyrrhiza (fugacious in older plants); this basal portion and its connecting stalk correspond to a condensed shoot that has become greatly reduced through evolution; 2 lateral budding pouches on either side of basal end; daughter plants and smaller, overwintering turions produced in budding pouches; raphide and druse crystals of calcium oxalate throughout parenchyma, and scattered brown epidermal pigment cells (visible on dead plants of Landoltia punctata); 2-several roots near center of ventral side (with minute root sheath at base), one or more roots penetrating the membranous ventral lobe of scalelike prophyllum; one bisexual flower produced within membranous spathe (utricular scale) inside each lateral budding pouch, consisting of a single pistil flanked by 2 stamens (some authorities consider this to be an inflorescence with 3 unisexual flowers); anthers bilocular and transversely dehiscent; ovary unilocular with 1 amphitropous or 2-4 anatropous ovules; utricle globular and slightly compressed-winged, bearing 1-2 smooth or longitudinally-ribbed seeds; 3 spp. worldwide; from the Greek speira, cord or thread, and delos, evident or visible, referring to fascicles of roots; Daubs (1962), Rhodora 64: 83-85; Daubs (1965), Illinois Biol. Monogr. 34: 1-118; Armstrong, W.P. (1984), Madrono 31: 123-124.

1   D.H. Les and D.J. Crawford (1999) proposed the new genus Landoltia containing one species L. punctata, formerly Spirodela punctata (G.F.W. Meyer) C.H. Thompson. This species is morphologically intermediate between Lemna and Spirodela. According to Les & Crawford, it represents an isolated clade distinct from both Lemna and Spirodela. Les, D.H. and D.J. Crawford. 1999. "Landoltia (Lemnaceae), A New Genus of Duckweeds." Novon 9: 530-533.

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