Sp. Pl. 2: 1062. 1753; Gen. Pl. ed. 5, 484, 1754.
Plants terrestrial. Roots unbranched, whitish yellow to black, 0.1-1.5 mm diam., smooth, commonly proliferous and forming clones. Stems upright, forming caudex, to 1.6cm thick (cormlike in O. crotalophoroides); gemmae absent. Trophophores erect to prostrate, blades nearly sessile or stalked, lanceolate to cordate, simple, 0.4-100 mm × 0.3-45 mm; margins entire; apex rounded, acute, or apiculate; veins anastomosing, main areoles to 15 × 4mm, but mostly less than 5 × 3 mm. Sporophores 1 per leaf, simple, stalked, borne from ground level to well above ground at base of trophophore but commonly absent, leaf made up of only trophophyll. Sporangial clusters with sporangia in 2 rows, deeply sunken in simple, linear or oblong fleshy sporophore tip, tip usually ± apiculate. Gametophytes brown to white, narrowly linear, unbranched, 2-20 × 1-3mm diam. x =30.
Nearly worldwide, mainly tropical and subtropical.
Ophioglossum occurs mostly in disturbed, open, grassy habitats. It is often overlooked because of superficial resemblance to seedlings of monocotyledonous plants. The intensive and careful field studies of R.D. Thomas (W. H. Wagner Jr., C. M. Allen, and G. P. Landry 1984) have greatly extended our knowledge of adder's-tongue distributions in North America. The chromosome numbers of Ophioglossum are the highest known in all vascular plants; numbers as high as 2n =1200+ have been reported (A.Löve et al. 1977).
(Key to species of Ophioglossum)
Species 25-30 (7 in the flora).
|1||Stems spheric, cormlike, fleshy, 3–12 mm diam.; leaves arising from deep cavity in top of stem; trophophore blades usually lying flat on ground, deltate to cordate.||Ophioglossum crotalophoroides|
|1||Stems upright, 1–5 mm diam., seldom more; leaves arising at top of stem; trophophore blades erect to spreading, mostly ovate to lanceolate.||> 2|
|2||Trophophore veins in larger leaves forming small areoles within larger areoles.||> 3|
|2||Trophophore veins forming only branching or nonbranching, free, included veinlets within larger areoles.||> 4|
|3||Blades commonly folded when alive, ovate to ovate-lanceolate, to 10 × 4.5 cm; roots 0.5–1.5 mm diam.; sporophores 1.3–2.5 times length of trophophore; dried blades uniformly green without pale central band.||Ophioglossum engelmannii|
|3||Blades plane when alive, ovate to lanceolate, to 4.5 × 1.7 cm; roots 0.2–0.8 mm diam.; sporophores 2–6 times length of trophophore; dried blades commonly with pale central band.||Ophioglossum nudicaule|
|4||Blades rounded at apex, apiculum absent, ovate-lanceolate, oblanceolate, ovate, to trowel-shaped, to 10 × 3.5 cm; adult leaves usually 1 per stem, appearing in a single flush once per year.||> 5|
|4||Blades acute at apex, with ± developed apiculum or apiculum absent, ovate-oblong, ovate-deltate, or ovate-lanceolate, to 4.5 × 1 cm (6 × 3 mm occasionally in O. petiolatum); adult leaves commonly 2–3 per stem, appearing in 1 or more flushes per year, depending on rains.||> 6|
|5||Blades dark green, somewhat shiny (alive), ovate to trowel-shaped, firm, base abruptly tapering; damp forest habitats; se United States, Mexican highlands.||Ophioglossum vulgatum|
|5||Blades pale green, dull (alive), obovate to oblanceolate or ovate, herbaceous, base gradually tapering; open pastures, meadows, marshes, ditches; n North America.||Ophioglossum pusillum|
|6||Roots dark brown, usually fewer than 8 per shoot, major roots generally straight, 0.8–1.3 mm diam.; blade apiculum mostly absent; venation usually coarse.||Ophioglossum petiolatum|
|6||Roots yellowish to pale brown, usually more than 12 per shoot, 0.2–1 mm diam.; blade apiculum absent or present; venation usually fine, intricate.||> 7|
|7||Roots 0.5–1 mm diam.; sporophores 1–2.5 times length of trophophore; trophophores 0.4–4.3 × 0.3–1 cm, commonly folded when alive; blades thick, herbaceous; California.||Ophioglossum californicum|
|7||Roots 0.2–0.8 mm diam.; sporophores 2–6 times length of trophophore; trophophores as small as 0.4 × 0.3 cm, usually plane when alive; blades thin, herbaceous; se United States.||Ophioglossum nudicaule|