Fig. 543: Ammannia teres: a, seed, front view, much enlarged; b, seed, side view, 

 X 75. (Courtesy of R. K. Godfrey). 



petals none; stamens 4; style abbreviated; capsule globose, 2-celled, indehiscent, 

 about 2 mm. in diameter. Didiplis diandra (Nutt.) Wood. 



In shallow water and on margin of water of ponds, streams and lakes in e. Tex. 

 and Okla. (McCurtain Co.), Mar.-June; from Fla. to Tex., n. to Va., O., Ind. 

 and Wise. 



6. Rotala L. 



Small annual herbs, glabrous or nearly so; leaves opposite, narrow; flowers regular 

 or nearly so, axillary, mostly solitary, small, bibracteolate; calyx with appendages 

 shorter to longer than the regular teeth; petals 4 or wanting; ovary ellipsoid; valves 

 of the capsule minutely transverse-striate. 



About 50 species, widespread mostly in tropical or subtropical regions. 



1. Bractlets usually shorter than the calyx; appendages half as long as to about 

 equal to the calyx teeth; ovary subovoid-globose 1. R. ramosior. 



1. Bractlets often twice as long as the calyx; appendages often 3 times as long 

 as the calyx teeth; ovary ellipsoid 2. R. dentifera. 



1. Rotala ramosior (L.) Koehne. Tooth-cup. Fig. 544. 



Small annual herb, low and sprawling to erect and spreading, with simple or 

 diffusely branched 4-angled stems, glabrous, to 45 cm. high, usually much smaller; 

 leaves opposite, subsessile to somewhat petioled, linear-oblong to elliptic or oblan- 

 ceolate, obtuse, to about 45 mm. long and 1 cm. wide; flowers regular or nearly so, 

 small, solitary in leaf axils, 4-merous, bibracteolate; calyx with appendages shorter 

 to longer than the teeth, the tube campanulate to globose; petals 4, attached to rim 

 of calyx tube, white or pink; stamens 4, attached low on calyx tube; capsule glo- 

 bose, 4-celled, enclosed in the membranous calyx, the valves minutely transverse- 

 striate, to 5 mm. long and 4.5 mm. broad, the somewhat persistent style about 0.5 

 mm. long; bractlets linear-lanceolate to subulate, to 4 mm. long. 



In sandy or muddy soil in water or on the edge of ponds, lakes, tanks and in 

 depressions in the e. half of Tex., Okla. (LeFlore, Comanche, Johnston, McCur- 

 tain, Ottawa and Carter cos.) and Ariz. (Cochise Co.), May-Oct.; from Fla. to 

 Tex. and Ariz., n. to N.E., N.Y. and the Lake States; also Wash, and Ore. 



Most of our material is referable to var. interior Fern. & Grisc. This is a more 

 robust and upright plant than var. ramosior. The larger leaves are usually subsessile 

 and are 5-10 mm. wide, the capsules are 3.5-5 mm. long and 3.2-4.5 mm. broad, 

 and the linear-lanceolate bractlets are 1.6-4 mm. long. These organs in var. 

 ramosior have smaller measurements. 



2. Rotala dentifera (Gray) Koehne. Fig. 545. 



Stems erect or ascending, 3-50 cm. long; herbage glabrous; leaves lanceolate- 

 elliptic to oblanceolate, narrowed to a very short petiole or subsessile, 2-4 cm. long; 

 flowers sessile and solitary in the leaf axils; bracts linear to linear-lanceolate, accres- 



1164 



