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Ferns

Ferns (Class Polypodiopsida) are seedless vascular plants that comprise the sister group (closest evolutionary relatives) to the seed plants (cycads, conifers, gnetophytes, Ginkgo, and flowering plants). Ferns first appear in the fossil record 360 million years ago in the Devonian, and many of the living families of ferns occur in the fossil record as early as 145 million years ago in the early Cretaceous. Ferns are similar to seed plants in having complex compound stems (called rhizomes in ferns), and large and complex megaphyll leaves (called fronds in ferns). Ferns differ from seed plants in that dispersal occurs as spores (as opposed to seeds) and in having separate gametophyte and sporophyte generations (as opposed to having compound reproductive organs with the female gametophyte embedded in the flower or cone).

The basic fern body plan comprises roots feeding a rhizome that bears fronds, which in turn bear sporangia. The sporangia may be solitary, fused into synangia, or grouped in clusters called sori. In most ferns, the sporangia are borne on the undersurface of the frond, but in some ferns, e.g. Ophioglossaceae, they are arranged in other ways such as specialised branches or clusters. Fern rhizomes are extremely variable, ranging from short, erect rhizomes that produce a rosette (or ring) of fronds to long creeping rhizomes that bear fronds spaced out along their length. Fern fronds also vary greatly, ranging from simple transparent membranous leaves 5 mm long in some Hymenophyllum to massive, tripinnate fronds up to 6 m long in Angiopteris evecta. The basic parts of a fern frond are: stipe (similar to the petiole of a flowering plant), costa or rachis (main axis of a simple or compound fern lamina), lamina, pinnae or pinnules (segments of a simple or compound fern frond), sporangia, paraphyses (hairs or scales among sporangia), and an indusium or false indusium (a flap or covering over the immature sporangia). Additional important features include hairs and scales, which can be very diagnostic in many families.

Australia is home to 4 classes, 11 orders, 29 families, 121 genera and 468 species and infraspecies of ferns, a majority of which occur in tropical Australia. No families or genera of ferns are restricted to Australia, probably because they are an ancient and highly dispersible group which has had a long time and a lot of opportunity to spread between landmasses.

Lycophytes

Lycophytes (Class Lycopodiopsida) are seedless vascular plants that are the sister group to ferns and seed plants. Lycophytes first appear in the fossil record 425 million years ago in the Silurian, making them the oldest recognisable class of vascular plant still living today. Most of the living diversity is considerably younger, however - most of the extant genera arose in the Cretaceous and species ages are comparable to many angiosperms. Lycophytes have the same life cycle as ferns, with free dispersal of spores and separate gametophyte and sporophyte generations. For this reason, they have been historically regarded as ‘fern allies’ even though ferns are more closely related to seed plants.

The basic lycophyte body plan comprises simple (unbranched) or dichotomously branched roots feeding a central, simple or dichotomously branched axis that bears simple, single-veined leaves called microphylls. The sporangia are relatively large, solitary and are positioned in the axils of upper microphylls. Lycophytes lack many features (such as hairs and scales) that are found in ferns. Their simple morphology makes species identification relatively difficult compared to ferns and seed plants, requiring the examination of many subtle or microscopic characters.

Australia is home to 2 subclasses, 3 orders, 3 families, 12 genera and 56 species of lycophytes. They are distributed broadly across tropical and temperate Australia and range in form and ecology from tiny aquatic plants (Isoetes) to large, hanging, epiphytic plants (Phlegmariurus).

Taxonomy and Nomenclature used

This key uses the nomenclature of Field (2020) which is based on the Pteridophyte Phylogeny Group classification (PPG I, 2016) with some updates from Field & Bostock (2020). This classification represents a substantial modernisation of the classification in the Flora of Australia 48 (McCarthy, 1998). These changes have occurred largely in response to great advances in the understanding of fern evolution and diversity arising from recent molecular phylogenetic studies. The circumscriptions of several families and many genera have been updated, including Blechnaceae, Dryopteridaceae, Lycopodiaceae, Pteridaceae and Thelypteridaceae. Work in this field is ongoing, involving an international collaborative team of researchers. As with all taxonomic research, further name changes may be required as new evolutionary data is published and as more historic materials come to light. It is intended this key will be updated to current nomenclature biennially.