234 FLORA. 



2. Wolffia punctata Griseb. PUNCTATE WOLFFIA. (I. F. f. 891.) Thallus 

 oblong, smaller than the last, 0.5-0.8 mm. long, flattish, densely cellular, with 

 numerous stomata and dark green above, gibbous, more loosely cellular, with 

 fewer stomata and paler beneath; brown-dotted throughout with minute pigment 

 cells. Floating on the surface of stagnant waters, Ont. to Mich, and Penn. June- 

 July. (W. Brasiliensis Engelm., not Wedd.) 



3. Wolffia papuhfera Thompson. POINTED DUCKWEED. (I. F. f. Sgia.) 

 Thallus slightly unsymmetrical, obliquely broadly ovate, about I ntfki. broad, the 

 apex rounded, the upper surface flat at the margin, gradually ascending into a 

 prominent conic papule on the median line, brown-punctate, the under surface 

 strongly gibbous, less punctate; stomata numerous on the upper surface; flower 

 and fruit unknown. Floating, with the entire upper surface exposed to the air. 



' Kennett and Columbia, Mo. 



4. WOLFFIELLA Hegelm. 



Thallus thin, unsymmetrical, rootless, curved in the form of a segment of a "band, 

 punctate on both surfaces with numerous brown pigment-cells. Pouch opening as 

 a cleft in the basal margin of the thallus, a stipe attached to its margins. Flowers 

 and fruit unknown. [Diminutive of IVolffia.] About 7 species, mostly of tropical 

 regions. Besides the following, 2 others are known from western North America. 



i. Wolffiella Floridana (J. D. Smith) Thompson. FLORIDA WOLFFIELLA. 

 (I. F. f. SSga.) Thallus solitary, or commonly coherent for several generations, 

 forming densely interwoven masses, strap-shaped, scythe-shaped, or doubly curved, 

 tapering from the rounded oblique base to a long-attenuate apex, 5-10 mm. long, 

 1421 times as long as wide; basal portion of the long stipe persistent, the poach 

 elongated-triangular, or the upper angle rounded. Ga. and Fla. to Mo., Ark. and 

 Tex. 



Order 7. XYRIDALES. 



Monocotyledonous herbs, mostly with narrow leaves. Flowers usually 

 complete, their parts mostly in 3's or 6's. Corolla regular or nearly 

 so (except in Commelina). Ovary compound, superior. Endosperm of 

 the seed mealy. 



a. Ovary i -celled. 



Aquatic moss-like leafy herbs; flowers solitary. Fam. i. Mayacaceae. 



Erect scapose rush-like herbs ; flowers in terminal scaly heads or spikes. 



Fam. 2. Xyridaceac. 

 Mud or aquatic herbs, the flowers subtended by spathes {Heteranthera in Ponte- 



deriaceae). 

 6. Ovary 2-3-celled (except in some Pontederiaceae). 



Flowers very small, densely capitate, monoecious or dioecious. 



Fam. 3. Eriocaulaceae. 

 Flowers perfect. 



Epiphytes ; leaves scurfy. Fam. 4. Bromeliaceae. 



Terrestrial or aquatic herbs; leaves not scurfy. 



Perianth of 2 series of parts, the outer (sepals) green, the inner (petals 



colored. Fam. 5. Commelinaceae.l 



Perianth 6-parted. Fam. 6. Pontederiaceae. 



Family i. MAYACACEAE Walp. 



Mayaca Family. 



Slender branching aquatic moss-like herbs, with linear sessile i-nerved 

 entire soft leaves, notched at the apex. Flowers solitary, peduncled, 

 white, perfect, and regular, the peduncles bracted at the base. Perianth 

 persistent, consisting of 3 lanceolate green herbaceous sepals and 3 obo- 

 vate white spreading petals. Stamens 3, hypogynous, alternate with the 

 petals ; filaments filiform ; anthers oblong, somewhat 4-sided, 2-celled. 

 Ovary superior, sessile, i -celled with 3 parietal placentae ; ovules several 

 or numerous, orthotropous ; style filiform; stigmas terminal, entire or 

 with 3 short lobes. Capsule i -celled, 3-valved. Seeds ovoid or globose, 



