62 LEMNACEAE. 



Order 7. ARALES. 



Monocotyledonous herbs, mostly fleshy. Inflorescence in the Araceae 

 (which are not now known to be represented by any wild plants in the 

 Bahama flora although Schoepf records observing Arum sagittifolium and 

 Orontium aquaticum on New Providence in 1784) a fleshy spadix, sub- 

 tended by a spathe, or naked. The Lemrwceae are minute floating thalloid 

 plants, with flowers on the margin or back of the thallus. 



Family 1. LEMNACEAE Dumort. 



DUCKWEED FAMILY. 



Minute perennial floating aquatic plants, without leaves or with only 

 very rudimentary ones. The plant-body consists of a disk-shaped, elon- 

 gated or irregular thallus, which is loosely cellular, densely chlorophyl- 

 lous and sometimes bears one or more roots. The vegetative growth is 

 by lateral branching, the branches being but slightly connected by slender 

 stalks and soon separating. The inflorescence consists of one or more 

 naked monoecious flowers borne on a slight lateral prominence on the edge 

 or upper surface of the plant. Each flower commonly consists of but a 

 single stamen or a single flask-shaped pistil. The anther is provided with 

 two to four pollen-sacs, containing spherical minutely barbellate grains. 

 The pistil is narrowed to the funnel-shaped scar-like stigmatic apex, and 

 produces 1-6 erect or inverted ovules. The fruit is a 1-6 seeded utricle. 

 The family comprises the smallest of the flowering plants and contains 4 

 genera and about 30 species of wide distribution. 



1. LEMNA L. Sp. PI. 970. 1753. 



Thallus disk-shaped, usually provided with a central nerve and with or 

 without two or four lateral nerves. Each thallus produces a single root, which 

 is devoid of vascular tissue and is commonly provided with a thin blunt or 

 pointed rootcap. The ovary contains from one to six 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 10 species, in tem- 

 perate and tropical regions. Type species: Lemna trisulca L. 



1. Lemna minor L. Sp. PI. 970. 1753. 



Thallus obovate or subcircular, 1.5-5 mm. long, thickish, rarely reddish 

 or purplish tinged, short-stalked when young, provided throughout with 

 etomata, nearly symmetrical, obscurely 3-nerved, very rarely 4-5-nerved. Root- 

 cap obtuse or subtruncate; fruit symmetrical, subturbiuate ; seed with a 

 prominent protruding hilum, deeply and unequally 12-15-ribbed; ovule 1. 



Water-holes and sink-holes, near The Bight, Cat Island : North temperate and 

 subtropical zones, but not known to us elsewhere in the West Indies. DUCK-WEED. 



