1. S. spinòsa, Beauv. Sterile stems prostrate or creeping, small and slender; the fertile thicker, ascending, simple (1–3´ high); leaves lanceolate, acute, spreading, sparsely spinulose-ciliate. (S. selaginoides, Link.)—Wet places, N. H. (Pursh), Mich., Lake Superior, Colorado, and northward; rare.—Leaves larger on the fertile stems, yellowish-green. (Eu.)
2. S. rupéstris, Spring. ([Pl. 21], fig. 1–4.) Much branched in close tufts (1–3´ high); leaves densely appressed-imbricated, linear-lanceolate, convex and with a grooved keel, minutely ciliate, bristle-tipped; those of the strongly quadrangular spike rather broader.—Dry and exposed rocks; very common.—Grayish-green in aspect, resembling a rigid Moss. Very variable farther west and south. (Eu.)
[*][*] Leaves shorter above and below, stipule-like; the lateral larger, 2-ranked.
3. S. àpus, Spring. Stems tufted and prostrate, creeping, much branched, flaccid; leaves pellucid-membranaceous, the larger spreading horizontally, ovate, oblique, mostly obtuse, the smaller appressed, taper-pointed; those of the short spikes nearly similar; larger spore cases copious at the lower part of the spike.—Low, shady places; not rare, especially southward.—A delicate little plant, resembling a Moss or Jungermannia.
2. ISÒETES, L. Quillwort. ([Pl. 21.])
Stem or trunk a fleshy more or less depressed corm, rooting just above its 2-lobed (or in many foreign species 3-lobed) base, above covered with the dilated and imbricated bases of the awl-shaped or linear somewhat quadrangular leaves, which include four air-tubes, intercepted by cross partitions. Sporangia pretty large, orbicular or ovoid, plano-convex, very thin, sessile in the axils of the leaves, and united at the back with their excavated bases (the thin edges of the excavation folding round partly cover them, forming the velum), traversed internally by transverse threads; those of the outer leaves filled with large spherical macrospores, their whitish crustaceous integument marked by one circular, and on the upper surface by three radiating elevated lines (circumscribing a lower hemisphere, and three upper segments which open valve-like in germination); those of the inner leaves filled with very minute and powdery grayish microspores; these are always obliquely oblong and triangular.—Mostly small aquatics, grass-like or rush-like in aspect, some always submerged, others amphibious, a few living in merely moist soil, maturing their fruit in late summer and early autumn, except n. 7 and some forms of n. 6.
This genus is left essentially as it was elaborated for the 5th edition by the late Dr. George Engelmann. The present editor has added to the range of a few species, and given var. robusta of n. 3.
[*] Growing under water, only accidentally or in very dry seasons out of water; leaves without stomata (except in forms of n. 3) and peripherical bast-bundles.
1. I. lacústris, L. ([Pl. 21], fig. 1–5.) Leaves (10–25 in number, 2–6´ long) dark green, rigid; sporangium ovoid or circular, the upper third, or less, covered by the velum, the free part pale and unspotted; both kinds of spores the largest of our species; macrospores (0.32–0.38´´ wide) covered with short and twisted crested ridges, which often anastomose; microspores (0.017–0.020´´ long) smooth.—Mountain lakes, Penn., N. Y., and New Eng. to Lake Superior, and northward, often with n. 3. (Eu.)
2. I. Tuckermàni, Braun. Leaves (10–30, 2–3´ long) very slender, awl shaped, olive-green, the outer recurved; sporangium ovoid or circular, the upper third covered by the velum, the free part sometimes brownish-spotted; macrospores (0.22–0.28´´ wide) on the upper segments covered with parallel and anastomosing ridges, the lower half reticulated; microspores (0.013–0.015´´ long) smooth or very delicately papillose.—Mystic and other ponds near Boston, together with the next (Tuckerman, W. Boott).