Ferns and lycophytes abound in New Zealand’s rainforests. In the humid interior they carpet forest floors, and climb and perch on tree trunks and branches. Tall, graceful tree ferns line the sides of streams and dominate in damp gullies. Outside the forest, ferns are also conspicuous. Many roadside banks and damp hillsides are covered in a luxurious growth of kiokio (Blechnum novae-zelandiae). Bracken (Pteridium esculentum) and ring fern (Paesia scaberula) form extensive stands in open country, and on the coast hardy ferns like shore spleenwort (Asplenium obtusatum) grow on exposed cliff faces.
Changing fronds
Thread ferns (Blechnum filiforme) begin life on the ground, where they scramble around until they find a trunk to climb. On the ground they produce only short fronds with rounded segments, but as they grow upwards their fronds become larger, with more elongated segments. Finally, well above head height, they produce fertile fronds with very slender segments. The lower fronds appear so different from the upper fronds that people mistake them for different species.
What are ferns and lycophytes?
Ferns and lycophytes are green plants that lack flowers. They reproduce by microscopic spores, rather than by seeds as in flowering plants or conifers. What distinguishes them from the other spore-producing land plants such as mosses or liverworts is that their life cycle involves two separate, independent phases: a leafy plant phase that produces spores; and an inconspicuous, short-lived plant that bears sex organs. It is the leafy, spore-producing plant most people think of as a typical fern or lycophyte.
Structure
Ferns and lycophytes typically have three main parts:
- Stems. There are various types, including creeping or climbing ones with widely spaced fronds, short or compressed stems from which a crown of fronds arise, and the tall, upright stems of tree ferns.
- Fronds. There is usually a stalk with a flat blade divided into segments. New fronds are tightly coiled into a spiral, popularly known as fiddleheads or koru.
- Spore-producing structures or sporangia. Fertile fronds carry reproductive structures, sterile fronds do not.
Distinguishing ferns from lycophytes
Ferns
There is no single character that defines ferns. One large group is easily recognised by its highly divided fronds with branching veins and spore-bearing structures (sporangia) on the margins or undersides. The other group is not as leafy, and contains members that look quite different from each other. Some, such as fork ferns, whisk ferns and horsetails, were previously grouped with lycophytes and known as ‘fern allies’, but DNA evidence suggests they are actually ferns. Collectively, ferns belong to a group known as monilophytes.
Confusing common names
In the mid-18th-century the great Swedish botanist Linnaeus grouped clubmosses and spikemosses with true mosses. It took another 50 years or so before botanists realised that clubmosses and spikemosses were distinct from mosses, but by then they were stuck with common names that described them as types of moss.
Lycophytes
Lycophytes include clubmosses, spikemosses and quillworts. Their sporangia are on the upper surface of small leaves with unbranched veins. The leaves are spirally arranged around the stem. Lycophytes are of an ancient lineage, no more closely related to ferns than to seed plants, and therefore inappropriately called ‘fern allies’. They belong in their own subphylum equivalent to the rest of the vascular plants.