DUCKWEED FAMILY 315 



ARALES ARUM ORDER 

 LEMNACEAE DUCKWEED FAMILY 



Flowers rarely seen, consisting of a single stamen or a single pistil, fruit 

 a 1-6-seeded utricle; flowers monoecious, 1 or more on the edge or upper 

 surface of the plant ; plant a disk-shaped or irregular leaf-like body, usually 

 with 1 -several rootlets ; tiny, floating, aquatic perennials without true leaves. 



LEMNA Lyinne 1753 DUCKWEED 

 (Possibly from Gr. limne, lake) 



PL 44, fig. 5, 6. 

 Characters of the family. 



1. Plant body or thallus lanceolate, often connected 



in a chain L. trisulca 



2. Plant body or thallus elliptic to ovoid or round 



a. Thallus 3-5-nerved 



(1) Thallus more or less strongly swollen be- 



neath L. gibba 



(2) Thallus not swollen beneath 



(a) Thallus small, 2-3 mm. long, abruptly 



narrowed to a very short stalk L. perpusilla 



(b) Thallus 2-6 mm. long, not abruptly nar- 



rowed to a stalk L. minor 



b. Thallus not nerved 



( 1 ) Thallus thin, without pappules ; root-cap 



curved, tapering L. cydostdsa 



(2) Thallus thick, with a row of pappules, 



root-cap scarcely curved, cylindric L. minima 



HYDRALES WATERWEED ORDER 

 HYDROCHARITACEAE WATERWEED FAMILY 



Perianth of 6 parts, in 2 rows, at least the 3 inner petal-like, stamens 9, 

 ovary 1-celled with 3 placenta, stigmas 3, fruit closed, few-seeded; flowers 

 dioecious or polygamous from a 2-cleft spathe; submerged plants with op- 

 posite or whorled, crowded, entire or minutely toothed leaves. 



PHILOTRIA Rafinesque 1818 WATERWEED 

 (Gr. philos, loving, tria, three, the leaves often in 3's) 

 Characters of the family. 



Stems .5-3 ft. long; leaves linear to elliptic, usually 

 3-4 in a whorl, .5-1.5 cm. long P.canadensis 



