48 POACEAE 



FAMILY 2. HYDRO OH ABIT ACE AE Aschers. FROG'S-BIT FAMILY. 



Aquatic or mud-inhabiting herbs. Leaves clustered, usually with well de- 

 veloped blades. Flowers monoecious or dioecious, arising from spathes of distinct 

 or united bracts. Perianth regular, superior, of 3 sepals and 3 petals. Androe- 

 cium of 6-12 stamens. Filaments distinct or partially united. Gynoecium of 

 6-15 united carpels. Ovary inferior, usually 6-9-celled. Styles as many as the 

 cavities of the ovary. Ovules numerous. Fruit usually indehiscent. 

 Leaf not differentiated into blade and petiole : flowers dioecious : stamens distinct : anthers nearly 



sessile. 1. THALASSIA. 



Leaf differentiated into blade and petiole : flowers monoecious : stamens with united 



filaments. 2. LIMNOBIUM. 



1. THALASSIA Banks. 



Marine herbs, with elongated rootstocks. Leaves several at a joint, sheathing at the base : 

 blades linear, elongated. Scape arising from the cluster of leaves. Flowers dioecious, solitary 

 in narrow spathes of two bracts : these united into a tube at the base. Staminate flowers long- 

 pedicelled : perianth of 3 petaloid sepals : stamens 6 : filaments very short : anthers open- 

 ing laterally. Pistillate flower nearly sessile in the spathe, caducous : ovary 6-9-celled, 

 beaked. Fruit stalked, rugose or nearly echinate, opening by many valves. Seeds numerous. 



1. Thalassia testudinum Koenig & Sims. Submersed, glabrous. Rootstocks creep- 

 ing, elongated : stems short, arising from the nodes of the rootstock : leaves 2-5, sheathing 

 the stem ; blades linear, strap-like, 0.5-3 dm. long, obtuse, withering-persistent : scapes 

 solitary, central : fruit globose or oval, echinate-pubescent, slightly pointed. 



In shallow water, along the coast of peninsular Florida. Also in the West Indies. 



2. LIMNOBIUM L. C. Rich. 



Aquatic herbs usually floating and producing pendent roots and stolons. Leaves 

 clustered : petioles elongated : blades broad, several-nerved. Flowers monoecious, from 

 spathes of 2 membranous bracts. Perianth white : sepals 3 : petals 3, narrower than the 

 sepals. Staminate flowers 2-4 in a spathe, usually with 6-12 stamens : filaments united into 

 a column, bearing the anthers at different heights. Pistillate flowers with 3-6 abortive 

 stamens, a 6-9-celled ovary with several central placentae : stigmas as many as the cavities 

 in the ovary, each 2-parted. Fruit a many-celled berry. 



1. Limnobium Spongia (Bosc) L. C. Rich. Acaulescent, stoloniferous. Leaves 

 basal ; petioles erect or ascending, 5-25 cm. long : blades ovate to suborbicular or reniform, 

 2-5 cm. broad, obtuse, entire, truncate or cordate at the base ; petioles tapering to the 

 blade : flowers monoecious ; Staminate on scapes 8-10 cm. long ; pistillate on shorter and 

 stouter scapes, these recurving at maturity: berry nodding, oval, 1-1.5 cm. long. 



In shallow water or mud, Ontario to Illinois and Missouri, to Florida and Louisiana. FROG'S-BIT. 



Order 5. POALES. 



Mostly perennial caulescent or acaulescent plants, commonly known as 

 GRASSES and SEDGES. Stems (culms) simple or branched, sometimes conspicu- 

 ously jointed. Leaves alternate, mostly sheathing at the base : blades usually 

 narrow and elongated, entire or nearly so. Flowers variously disposed in a 

 simple or compound inflorescence, perfect, or rarely monoecious or dioecious, 

 incomplete, inconspicuous, in the axils of chaffy bracts or scales (glumes). 

 Fruit a caryopis (grain) or an achene. 



Leaves 2-ranked, their sheaths with ununited margins : stems mostly hollow : fruit a grain (caryopsis). 



Fam. 1. POACEAE. 

 Leaves 3-ranked, their sheaths with united margins : stems solid : fruit an achene. Fam. 2. CYPERACEAE. 



FAMILY 1. POACEAE R. Br. 1 GKASS FAMILY. 



Annual or perennial herbs, rarely shrubs or trees, sometimes monoecious or 

 dioecious, varying much in habit. Stems (culms) usually hollow, the nodes 

 closed. Leaves alternate, 2-ranked, sheathing, the sheaths generally open to 

 the base on the side opposite to the blade ; a scarious or cartilaginous ring 



1 Contributed by Mr. George V. Nash. 



