l.cmna.} PISTIACEJE. 



269 



1. Lemna. Linn. Duckweed. 



Perianth single, monophyllous, membranaceous, urceolate. 

 Fruit utricular. — Name, Xc/tipa, of the Greeks, from \ct-is, a 

 scale. Dktndria. Monogynia, 



1. L. trisulca, Linn. Ivy-leaved Duckweed. Fronds thin, 

 elliptico-lanceolate, caudate at one extremity, at the other ser- 

 iated ; roots solitary. Br. Fl. I. p. 12. E. Fl. v. up. 32. E. 

 Bot. t. 926. 



Clear stagnant waters. In the Boyne, near the bridge at Navan, 

 and many other places. Fl. July. 0. — Fronds from one-half to 

 three-fourths of an inch in length, pellucid at the margins, reticulated. 

 Hoots solitary, tipped at the extremity, with a small sheath. Hooker. 



2. L. minor, Linn. Lesser Duckweed. Fronds nearly ovate, 

 compressed ; roots solitary. Br. Fl. 1. p. 12. E. Fl. v. i. p. 

 32. E. Bot. t. 1095. 



Stagnant waters, common. Fl. July. 0. — About a line or a line 

 and a half long ; of a rather thick and succulent, but compact texture, 

 slightly convex beneath. " This is the most abundant of all the spe- 

 cies, covering the surface of ditches and ponds, and harbouring various 

 insects and molluscae, the food of ducks and other water-fowl, whence 

 the English name of Duckweed. The young fronds constitute the 

 Lemna arhiza of the French authors. The capsule is single-seeded ; 

 seed transverse, with its hilum " directed towards the narrow end of 

 the frond. Wilson." Hooker. The fruit of this species was first 

 pointed out to me at the lake near Sandymount, by W. Wilson, Esq. of 

 Warrington, in July, 1829. 



3. L. polyrhiza, Linn. Greater Duckiveed. Fronds obo- 

 vate, rotundate, compressed ; roots numerous, clustered. Br. 

 Fl. 1. p. 13. E. Fl. v. i. p. 33. E. Bot. t. 2458. 



Stagnant waters. Common about Limerick and elsewhere ; Mr. 

 W. II. Harvey. Flowers unknown in Britain. 0. — The largest of 

 all the species, half an inch long and nearly as broad, succulent, firm, 

 faintly striated ; a little convex below, where, and at the margin above, 

 it is of a deep purple colour. Roots numerous from a central point. 



4. L. gibba, Linn. Gibbous Duckweed. Fronds obovate, 

 nearly plane above, hemispherical beneath ; roots subsolitary. 

 Br. Fl. 1. p. 13. E. Fl. v. i. p. 32. E. Bot. t. 1233. 



Stagnant water, less frequent than the last. Fl. June — Sept. 0. — 

 Size of L. minor, but readily distinguished by its gibbous or even he- 

 mispherical lower surface, which is moreover white, pellucid, and 

 beautifully cellular, the cells filled with air, ( Wilson) ; upper side 

 plane, green, opaque. " Capsule four-seeded. Seeds furrowed, not 

 transversely placed, but with the hilum towards the top of the capsule." 

 Wilson, 



