Var. válida, Engelm. Trunk large and stout (often 1–2´ wide); leaves (50–100, even 200, 18–25´ long) with an elevated ridge on the upper side; sporangium oblong or linear-oblong (4–9´´ long), {1/3}–½ or more covered by the velum; spores very small; macrospores 0.16–0.22´´ wide; microspores 0.011–0.013´´ long, spinulose.—Del. (Canby) and Penn. (Porter). Sept.
7. I. melanópoda, J. Gay. Leaves (15–50, 6–10´ long) very slender, keeled on the back, straight, bright green, usually with dark brown or black shining bases; sporangium mostly oblong, with a very narrow velum, brown or spotted; macrospores very small (0.14–0.18´´ wide), smoothish, or with faint tubercles or ridges; microspores (0.010–0.012´´ long) spinulose.—Shallow ponds, and wet prairies and fields, central and northern Ill. (E. Hall, Vasey), and westward. June, and sometimes again in Nov.—Trunk more spherical and more deeply 2-lobed, and both kinds of spores smaller than in any other of our species; leaves disappearing during the summer heat. Closely approaching the completely terrestrial species of the Mediterranean region.
Order 135. MARSILIÀCEÆ.
Perennial plants rooted in mud, having a slender creeping rhizome and either filiform or 4-parted long-petioled leaves; the somewhat crustaceous several-celled sporocarps borne on peduncles which rise from the rhizome near the leaf-stalks, or are more or less consolidated with the latter, and contain both macrospores and microspores.
1. MARSÌLIA, L. ([Pl. 25.])
Submersed or emersed aquatic plants, with slender creeping rootstocks, sending up elongated petioles, which bear at the apex a whorl of four nervose-veined leaflets, and at or near their base, or sometimes on the rootstock, one or more ovoid sporocarps. These sporocarps or fruit usually have two teeth near the base, and are 2-celled vertically, with many transverse partitions, and split or burst into 2 valves at maturity. The sporocarps have a ring along the edges of the valves, which at length swells up and bears the sausage-shaped compartments from their places. The compartments contain macrosporangia and microsporangia intermixed. (Named for Aloysius Marsili, an early Italian naturalist.)
1. M. quadrifòlia, L. Leaflets broadly obovate-cuneate, glabrous; sporocarps usually 2 or 3 on a short peduncle from near the base of the petioles, pedicelled, glabrous or somewhat hairy, the basal teeth small, obtuse, or the upper one acute.—In water, the leaflets commonly floating on the surface; Bantam Lake, Litchfield, Conn., and now introduced in many places. (Eu.)
2. M. vestìta, Hook. & Grev. Leaflets broadly cuneate, usually hairy, entire (2–7´´ long and broad); petioles 1–4´ long; peduncles free from the petiole; sporocarps solitary, short-peduncled (about 2´´ long), very hairy when young; upper basal tooth of sporocarp longest, acute, straight or curved, lower tooth acute, the sinus between them rounded. (M. mucronata, Braun.)—In swamps which become dry in summer; Iowa and southwestward.
Order 136. SALVINIÀCEÆ.
Floating plants of small size, having a more or less elongated and sometimes branching axis, bearing apparently distichous leaves; sporocarps or conceptacles very soft and thin-walled, two or more on a common stalk, one-celled and having a central, often branched receptacle which bears either macrosporangia containing solitary macrospores, or microsporangia with numerous microspores.