1. Glochidia with several scattered septa; basal portion of the megaspore pitted; 

 plant usually more than 1 cm. in diameter; leaves 0.7 mm. long or 

 more, closely imbricate 1. A. mexicana. 



1. Glochidia without septa or rarely with 1 or 2 septa mostly just beneath the 



tip (2) 



2(1). Plants elongate, 2 cm. long or more; leaves oblong to ovate, closely ap- 

 pressed and imbricate, papillose, about 1 mm. long; basal portion 

 of the megaspore tesselate-reticulate 2. A. filiculoides. 



2. Plants small, to 1 cm. in diameter; leaves suborbicular, divaricate, nearly 



smooth, about 0.5 mm. long; megaspore unknown 



3. A. caroliniana. 



1. Azolla mexicana Presl. Fig. 12. 



Plants flattened, dichotomously branched, 1-3 cm. in diameter; upper leaf 

 lobes imbricated, somewhat irregular in shape, usually broadly rhombic-ovate to 

 suborbicular, broadly rounded to obtuse at apex, mostly less than 1 mm. long, 

 usually profusely tinged purplish-cerise, papillose, with narrow hyaline cellular- 

 papillose margins, under leaf lobes usually much larger than the upper ones; 

 microsporangia usually with 4 massulae; megaspores pitted on the basal portion; 

 glochidia of massulae always septate. 



Floating on surface of lakes and ponds and in quiet waters of streams and 

 irrigation canals in the Rio Grande Valley of s. Tex. and in N.M.; from s. Tex., 

 Calif, and Mex., s. to n. S.A., n. to Ut., B.C., Wise, and 111. 



2. Azolla 'filiculoides Lam. Fig. 12. 



Plants elongate, dichotomously branched, 2-6 cm. long; upper leaf lobes closely 

 appressed, imbricated, minutely papillose, oblong to ovate, obtuse at apex, about 

 1 mm. long, with rather broad thin hyaline margins that are usually only slightly 

 cellular-papillose, brownish and somewhat sparingly tinged with red; under leaf 

 lobe about as large as the upper one; microsporangia with 4 to 6 massulae; 

 megasporangia with the basal portion tesselate-reticulate; glochidia of massulae 

 not septate or rarely septate only at the apex. 



In fresh-water ponds and ditches in Ariz. (Pima, Santa Cruz, Mohave and 

 Yuma cos.) ; from Alas, to Guat.; also S.A., Eur. and H.I. 



3. Azolla caroliniana Willd. Fig. 13. 



Plants forming floating mats to 3 cm. across; leaves minute, deeply bilobed, 

 imbricate, mostly with hyaline margins, to 0.9 mm. long and 0.6 mm. wide, the 

 upper emersed lobes oval or suborbicular-quadrate, deep-green to purplish-red, 

 somewhat convex, hollow, provided with numerous 2-celled hairs, the lower sub- 

 mersed lobes glabrous, larger and paler than the upper lobes. 



On still water of swamps, ponds, lakes and in slow-moving water of streams 

 and resting on mud, up to 5,500 ft. alt., Okla. (McCurtain Co.) and in Tex. 

 sporadically distributed from Wood Co. in the n.e. Timber Belt, s. to Orange 

 Co. on the Coastal Prairies and Cameron Co. in the Rio Grande Plains, w. to 



Fig. 12: Azolla. a-e, A. mexicana: a, part of a fertile plant: (left) globose micro- 

 sporocarp with megasporocarp at its base, (right) pair of megasporocarps enclosed in 

 one indusium (uncommon), x 20; b, habit, top view, x 12; c, septate glochidia of 

 microsporia massulae, x 100; d, microsporic massula, x 40; e, megaspore covered by 

 tip of indusium, X 40. f-1, A. filiculoides: f, megaspore covered by tip of indusium, 

 X 40; g, young stalked microsporangia, showing a few glochidia of the massulae pro- 

 truding from ruptured wall, 40; h, separating massulae, x 40; i, nonseptate glochidia, 

 X 100; j, microsporocarp containing a large number of microsporangia (from same 

 plant as k), x 20: k, part of fertile plant viewed from below and showing the roots 

 and a small microsporocarp with a megasporocarp at its base, x 20; 1, separating 

 massulae, x 40. (From Mason, Fig. 6.). 



59 



