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Group 1: Lycophytes, Monilophytes
See list of 21 families in this group-
1a. Stems conspicuously jointed, bearing at each joint a small whorl of black or red-brown leaves (sometimes white-margined) that are united at the base; sporangia aggregated in a terminal strobilus [Fig. 25], borne on the underside of peltate sporangiophores
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1b. Stems not conspicuously jointed, the leaves not arranged in distinct and remote whorls; sporangia aggregated in a terminal strobilus or not, but never borne on peltate sporangiophores
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2a. Leaves or entire plant floating on the surface of the water (or stranded on mud as water levels decline); sporangia borne in sporocarps
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3a. Plants rooted in the substrate, with 4-parted, clover-like leaves
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3b. Plants free-floating, with simple leaves
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4a. Floating leaf blades mostly 5–15 mm long, with abundant and conspicuous branched hairs on the upper surface
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4b. Floating leaf blades 0.5–0.6 (–2) mm long, papillose, but lacking hairs on the upper surface
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2b. Leaves not floating on surface of water (though often borne below the surface in Isoetaceae); sporangia borne on the surface of leaves, sometimes ± concealed
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5a. Leaves narrow, with unexpanded, grass-like or quill-like blades; sporangia embedded in the leaf bases near the surface of the substrate [Fig. 7]; plants aquatic
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5b. Leaves various, but not quill-like; sporangia variously positioned, but usually elevated above the substrate; plants of upland or wetland communities
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6a. Plants entirely filamentous, forming felt-like colonies on rock, in caves, and under sheltered overhangs
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6b. Plants not filamentous, with moss-like or fern-like aspect, on various substrates
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7a. Leaves small, up to 1.1 cm long, scale-like, with a single midvein; sporangia usually aggregated in a terminal strobili (arranged in alternating zones on the shoot in the Huperziaceae)
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8a. Strobili quadrangular in cross-section (terete in Selaginella selaginoides); leaves with a small, adaxial ligule; spores of 2 sizes, the larger more than 0.3 mm wide
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8b. Strobili terete in cross-section or the sporophylls not aggregated into a strobilus; leaves without a ligule; spores of 1 size, less than 0.05 mm wide
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9b. Sporophylls arranged in alternating zones on the shoot [Fig. 2], unstalked, without lateral membranes, remaining green for the life of the plant; gemmiphores produced on mature plants; plants isotomously branched
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7b. Leaves 1–200 cm long, foliaceous, prominently veined; sporangia variously organized, but not borne in terminal strobili
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10a. Plants vines, with palmately lobed leaf blades
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10b. Plants not vines, the leaf blades unlobed, pinnately lobed, or pinnately divided
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11a. Sporangia thick-walled, lacking an annulus, commonly bearing more than 1000 spores; leaves not circinate in bud
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11b. Sporangia thin-walled, with an annulus, bearing up to 512 spores; leaves circinate in bud
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12a. Sporangium with an inconspicuous annulus composed of a group of apical, thick-walled cells on either side of the sporangial opening, bearing 256–512 spores; spore-bearing leaves or leaflets brown at maturity, conspicuously different from the vegetative leaves or leaflets
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12b. Sporangium with a well-developed annulus that forms a complete or nearly complete ring around the sporangium, usually bearing only 16–64 spores; spore-bearing leaves or leaflets normally green and similar to, or slightly different from, the vegetative leaves or leaflets (very different in Matteuccia and Onoclea)
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13a. Sori located at the leaf margin; indusium formed, at least in part, by a revolute leaf margin or portion of the margin (i.e., false indusium) [Fig. 33]; spores tetrahedral or tetrahedral-globose
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14a. Petiole apparently forking into 2 main divisions; sori borne on surface of the false indusium, this best viewed through dissection; ultimate segments without a distinct midrib (in part)
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14b. Petiole not appearing to fork into 2 divisions; sori borne on surface of leaf blade near margin and covered by false indusium; ultimate segments with a midrib
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15a. Leaf blade broad-deltate to ovate-deltate, (25–) 40–70 cm wide; nectaries present at base of leaf divisions, appearing as dark, oval areas in early season; base of petiole with 10 or more vascular bundles (in part)
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15b. Leaf blade narrow-oblong to lanceolate or broad-lanceolate, 1.5–18 cm wide; nectaries absent; base of petiole with 1 or 2 vascular bundles
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16a. Sori discrete, spherical, borne in circular or slightly bivalvate cups formed by fusion of the true indusium with the false indusium; false indusium merely a reflexed tooth or lobe (in part)
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16b. Sori becoming confluent as marginal bands, not borne in cup-like structures; false indusium formed by a ± elongate, revolute margin (in part)
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13b. Sori not located at the margin (except in Dryopteris marginalis) [Fig. 34]; indusium absent or present, but not formed by a revolute leaf margin (formed by a highly modified, revolute leaf margin in Matteuccia and Onoclea); spores oblong, reniform, bilateral, or winged
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17b. Sporangiasters absent; indusium usually present, sometimes inconspicuous (absent in Gymnocarpium and Phegopteris); leaves evergreen or deciduous, herbaceous to coriaceous, variously divided
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18a. Sori closely aligned in a single, chain-like row immediately adjacent to and on either side of the costa or costule (depending on the leaf division); indusium elongate and flap-like, opening toward the costa or costule (depending on leaf division); veins of leaf blade rejoining to form 1 or 2 (or more) rows of aereoles along the costa, then forking until meeting the margin
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18b. Sori variously arranged, when in rows parallel to the costa or costule then not immediately adjacent to them, rather on or adjacent to veinlets; indusium round to elongate, when elongate then opening away from the associated veinlet; veins of leaf blade unforked or freely forking, but not rejoining to form 1 or more rows of aereoles (except in Asplenium rhizophyllum)
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19a. Scales of the stem prominently clathrate-reticulate; indusia elongate and flap-like; petiole with 2 vascular bundles, these united distally into 1 X-shaped bundle
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19b. Scales of the stem not prominently clathrate-reticulate; indusia elongate and flap-like, circular, reniform, lacerate, or absent; petiole with 2–7 vascular bundles, when 2, united into 1 U-shaped bundle distally
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20a. Plants pubescent with needle-like, unicellular, transparent hairs (scales may be present as well)
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20b. Plants glabrous or pubescent, when pubescent the hairs pigmented, glandular, multicellular and/or flattened (these flattened “hairs” are actually microscales)
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21a. Leaves conspicuously dimorphic—fertile leaves bearing sporangia hidden by highly modified, indurate, revolute leaf segments and vegetative leaves either pinnately lobed (pinnate only at base) and with reticulate venation or vegetative leaves with lower leaflets greatly reduced in size compared with medial leaflets; spores green
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21b. Leaves monomorphic to weakly dimorphic; sterile leaves with simple or forking veins that do not rejoin, at least once-divided, and with basal leaflets that do not very gradually reduce in size; spores yellow or light brown to brown
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22a. Indusium inferior, composed of lacerate or filamentous segments at maturity; veins not reaching margin of leaf segments, ending in hydathodes near the margin; petioles articulated near base, this recognizable as a small, swollen node (not articulated in W. obtusa) (in part)
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22b. Indusium absent or present, sometimes inconspicuous, superior when present, attached centrally or laterally, not divided; veins reaching margin of leaf segments (except in Dryopteris); petioles not articulated near base
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23a. Indusium round to reniform; petiole base with 3–7 vascular bundles; teeth of leaf segments often bristle-tipped
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Each photo represents one family in this group.