640 ISOETACE^. 



1. SELAGINELLA, Beauv. 



Character;* of tlie ( )nlcr. 



1. S. rupestriS, Spring, stems rigid, densely clusteretl, erect or spread- 

 ing, imich l)ranclied; leavori (grayish) subulate, rigid, rougli-friugcd on the 

 margins, bristle-pointed, closely imbricated in many rows ; spiivus linear, nearly 

 sessile. — Dry sand ridges in the pine barrens, and on dry rucks, Florida, and 

 northward. — Stems 2' -3' high. 



2. S. apus, Spring. Sterna prostrate, creeping, slender, branched ; leaves 

 scattered, unetiual, tlie lateral ones larger and widely spreading, 2-ranked, 

 ovate, acute or obtuse, membranaceous, denticulate on the margins ; the others 

 smaller, acuminate, and appressed ; bracts of the short .sessile spike similar to 

 the leaves. — Low shady woods, Florida, and northward. — Plant whitish. 

 Stems 3' -9' long. 



Order 168. MARSILIACE^. 



Perennial mar.sh plants, from slender creeping rootstocks, and fili- 

 form, or 4-parted petioled leaves. Spores of two kinds, contained in a 

 2-valved transversely many-celled receptacle (sporocarp), which rises 

 from the rootstock or base of the petioles. 



1. MARSILIA, L. 



Plants with filiform creeping stems, a whorl of 4 wedge-shaped leaves at 

 the summit of a long erect petiole, and one or more globular sporocarps borne 

 on a slender stalk at the base of the petioles, each divided into several parti- 

 tions, wiiich contain the larger and smaller spoi'es. 



1. M. uncinata, A. Braun. Leaves smooth or hairy; sporocarps oval, 

 compressed, half as long as the peduncle. — Banks of the Mississippi below 

 Vicksburg. 



Order 169. ISOETACE^. 



Mostly aquatic or marsh plants, with filiform clustered leaves aris- 

 ing from a depressed 2-lobed trunk. Sporangia sunk in an excavation 

 of the dilated base of the leaves, either open, or covered by a fold of 

 the leaf {velum), filled with minute spores, the' central leaves bearing 

 lai'ger spores. 



1. ISOETES, L. 



Characters of the Order. 



\. I. flaccida, Shuttlw. Immersed; leaves very long (U°- 2°), slender, 

 flaccid, yellowish green ; spores very small, minutely pulverulent, not reticu- 

 lated. — In lakes and clear streams, Middle and West Florida. 



2. I. melanospora, Engelm. Small, mostly monoecious; leaves few 

 (5-10), distichous (2'-2^' long) ; spore cases covered by the thin edges of 

 the cavity {velum) ; larger spores blackish, very minutely warty, the smaller 



