a. Herbaceous plants with fundamentally dichotomous branching (although dichotomies may be unequal); Leaves without ligules, small, lacking leaf gaps, usually spirally arranged

b. Roots present; dichotomously branching

c. Sporangia eusporangiate, on adaxial surface of leaves (sporophylls) -- sporophylls either resembling ordinary foliage leaves or quite different and grouped in definite strobili

d. All spores the same size (homosporous)

e. Gametophytes developing outside the spore wall (i.e., exosporic), either green and photosynthetic or lacking chlorophyll and subterranean (with a fungal association); sperm biflagellate

f. "Living Fossils" -- a group that was much more common and diverse in the past (especially in the Carboniferous)

g. A family widely distributed; representatives: Lycopodium, Diphasiastrum, Lycopodiella, Hupersia, Pseudolycopodiella (all called club-mosses).

a. Herbaceous plants with fundamentally dichotomous branching (although usually unequally so); growth habit various; leaves small, lacking leaf gaps, alternate and mostly arranged in 4 rows along the stem and often of 2 distinct sizes, each leaf with a ligule (a small flap-like projection) on the adaxial side near the base

b. Roots dichotomously branching

c. Sporangia eusporangiate; on adaxial surface of sporophylls (in axil)

d. Sporophylls (modified leaves) in strobili, generally in 4 rows, of 2 kinds: microsporophylls bearing microsporangia (which produce small spores, i.e., microspores) and megasporophylls bearing megasporangia (which produce large spores, i.e., megaspores) -- heterospory

e. Gametophytes developing within the spore wall (endosporic) -- the megaspores producing female gametophytes and the microspores producing male gametophytes; sperm biflagellate

f. "Living fossils" -- a group that was much more common in the past (Carboniferous)

g. A family of a single genus, Selaginella, widely distributed, but tropical

a. Sporophyte with a dichotomously branching aerial and subterranean stem system; roots lacking, underground stems with rhizoids and with a fungal association assuming this function; aerial stems bearing scale-like leaves (probably reduced megaphylls)

b. Sporangia 2 or 3 chambered (probably compound), eusporangiate; sperm multiflagellate

c. All spores similar in size (homosporous)

d. Gametophyte subterranean, resembling a small piece of rhizome

e. Sporangia borne at the apex of small side-branches (appear to be arranged along the sides of the major stems of the plant -- sporophyte)

f. Probably related to eusporangiate ferns--reductions in association with mycorrhizal condition a family of 2 living genera, frequent throughout tropics; representative: Psilotum (wisk-fern)

a. Sporophytes (plants) herbaceous with jointed and ribbed stems; leaves small whorled (at node; probably reduced megaphylls), united at least at base into a sheath surrounding the stem; stem possessing various air cavities

b. Aerial stems with branches in whorls at the nodes; branches alternating with the leaves

c. Plants accumulate silica

d. Roots and erect stems developing from rhizomes (horizontal underground stems), roots not dichotomously branching, lateral root formation endogenous (thus plant body bipolar)--condition found in all of the following groups

e. Sporangia borne on specialized stalks (modified stems) which are organized into strobili

f. Spores all similar (homosporous) with elators (dispersing appendages which react to changes in atmospheric humidity), green

g. Gametophytes green, developing outside the spore wall; sperm multiflagellate

h. "Living Fossils" -- group was much more abundant and diverse in the past (Carboniferous) -- large tree-forms existed -- grew in forests which have produced much of our present day coal deposits

a. Herbs with pinnately compound (once or twice), uniform or dimorphic leaves (megaphylls -- as are all fern leaves)

b. Sporangia with several cell layers in the wall, large, scattered on surface of leaf, thin-walled, short stout stalked, globose, the annulus (an area of thick walled cells) limited to a small area on one side near apex, opening by a vertical slit originating at the annulus and extending over the top of the sporangium to the other side

c. A family of 3 genera, widely distributed from temperate to tropical areas; representative: Osmunda

a. "Tree ferns" -- up to 20 ft. tall -- palm like in habit

b. Sporangia leptosporangiate, with complete and horizontal annulus

c. A family of 3-7 genera, in tropical montane forests; representatives: Alsophila (tree-ferns), Cyathea

a. Ferns of very diverse habit

b. Sporangia leptosporangiate, usually in sori, naked or with a indusium (protection covering, true vs. false); sporangia with an incomplete vertical annulus (that is interrupted by the stalk of the sporangium); much variation in shape, size, and position of sori

c. An enormous family of about 170 genera, widely distributed; representatives: Adiantum (maidenhair fern), Pteridium (bracken), Pteris (brake), Polypodium (resurrection fern), Thelypteris, Woodwardia (chain fern)

d. Family often is divided up into a series of smaller groups, but as broadly defined in monophyletic; delimitation of segregate families is uncertain, and a broad concept is followed here, at until phylogenetic relationships within it are clarified, allowing the recognition of monophyletic subgroups.

a. Small, floating aquatics which are not fern-like in appearance; the leaves small, not circinate, often dimorphic

b. Heterosporous (producing 2 kinds of spores)

c. A family of 2 genera, widely distributed but most common in the tropics; representatives: Salvinia, Azolla; the latter often placed in its own family.