2. Lemna L. Sp. Pi. 970. 1753
Description
This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
2. Lemna L. Sp. Pi. 970. 1753
Thallus disc-shaped, usually provided with a central nerve and with or without two or four lateral nerves. Each thallus produces a single rootlet, which is devoid of vascular tissue and is commonly provided with a thin blunt or pointed rootcap. The ovary contains from one to six orthotropous, amphitropous or anatropous ovules. Fruit ovoid, more or less ribbed. Endosperm in one or three layers. [Greek, in allusion to the growth of these small plants in swamps.]
About 8 species, in temperate and tropical regions. Besides the following, Lemna angolensis is a native of Lower Guinea. Type species: Lemna trisulca L.
Thalli long-stipitate. | 1. | L. trisulca. |
Thalli short-stipitate or sessile. | ||
Spathe open. | ||
Thalli 1-nerved or nerveless. | ||
Thalli thin, without papules; rootcap strongly curved, tapering. | 2. | L. cyclostasa. |
Thalli thick, with a row of papules along the nerves; rootcap little curved, cylindric. | ||
3. | L. minima. | |
Thalli 3-nerved; rootcap cylindric. | 4. | L. perpusilla. |
Spathe sac-like. | ||
Thalli green or purplish beneath; fruit not winged. | 5. | L. minor. |
Thalli pale beneath, usually strongly gibbous; fruit winged. | 6. | L. gibba. |
1. Lemna Trisulca L. Ivy-Leaved Duckweed. Star Duckweed
Fig. 1121
Lemna trisulca L. Sp. PI. 970. 1753.
Thallus lanceolate, submerged and devoid of stomata in the primary aquatic form, ovate. to oblong-lanceolate, 6"-9' long, floating and provided with stomata in the later flowering stage. The later and more common form is narrowed at the base to a slender stipe, thin, denticulate, with or without rootlets, and slightly 3-nerved. Several individuals often remain connected, so as to form a chain-like series. Root-cap pointed; fruit symmetrical; seed deeply 12-15-ribbed.
In ditches, springs, ponds, shallow lakes and sloughs, Nova Scotia to British Columbia, south to New Jersey, New Mexico and California. Also in Europe, Asia, Africa and Australia. July-Aug.
2. Lemna Cyclostasa (Ell.) Chev. Valdivia Duckweed
Fig. 1122
L. minor cyclostasa Ell. Bot. S. C. and Ga. 2: 518. 1824. Lemna cyclostasa Chev. Fl. Paris 2: 256. 1827. Lemna valdiviana Philippi, Linnaea 33: 239. 1864.
Thallus oblong-elliptical, 1"- 1 1/2" long, thin, subfalcate-and shortly stalked at the base, provided with numerous stomata, except on the borders, nerveless; rootcap short-tapering, curved; spathe reniform; fruit ovoid-oblong, unsymmetrical; seed prominently 12-29-ribbed.
In pools and rivers, Massachusetts to Florida, west to Illinois, Wyoming and California. Also in Jamaica and in South America. June-July.
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