Hymenophyllum rarum facts for kids

Hymenophyllum rarum, also known as the narrow filmy-fern, is a type of fern from the Hymenophyllaceae family. This fern has very thin leaves and is often found in New Zealand and Tasmania. It grows in patches on rocks or as an epiphyte (meaning it grows on other plants like trees and tree ferns) in damp places like gullies or rainforests.

The narrow filmy-fern can handle some dry weather, so you might find it in exposed areas from the coast up to mountain regions. It forms wide, tangled patches with its long, creeping stems (called rhizomes) that have a few reddish-brown hairs. You can easily spot it by its thin, grey-green leaves, which have smooth edges. Its spore cases (sori) are tucked into the top parts of the upper leaves. This fern lives in rainforests across Tasmania, New South Wales, Victoria, and many islands of New Zealand.

What Does the Narrow Filmy-Fern Look Like?

The narrow filmy-fern is special because of its long, thin, creeping stem (rhizome) and its delicate, thin leaves (fronds). These fronds are a pale grey-green color, and the whole plant is smooth, meaning it has no hairs.

The fronds hang down and can be up to 15 cm long. The stalk (stipe) that holds the frond is very thin and black, about 20–70 mm long. The main stem of the leaf (rachis) has a wing-like edge near the top. The leaf blade (lamina) itself is divided once or twice, is pale green, and can be up to 100 mm long and 10–25 mm wide. Its edges are not toothed.

The fern's spore cases, called sori, grow one by one at the tips of the leaf segments. They are slightly sunken at their base. A group of leaf-like structures (bracts) surrounds the spore cases. A protective cover called an indusium completely covers the sporangia (where spores are made). When the spores are ready to be spread by the wind, this cover splits open.

Where Does the Narrow Filmy-Fern Live?

You can find the narrow filmy-fern in rainforests, where it forms patches on rocks. It often grows on trees and tree ferns in moist, sheltered valleys. This fern is spread widely across tropical and southern temperate areas. In Australia, it lives in New South Wales, Victoria, Tasmania, and the Bass Strait Islands. It is also very common throughout New Zealand, including the North and South Islands, as well as Stewart, Chatham, and Auckland Islands.

This fern grows in many different places, from coastal areas to mountains. It is common in rainforests, dense bushes (scrub), shaded cliff faces, or among large rocks in damp valleys. It often grows alongside other filmy-ferns. It looks a lot like its relatives, H. cupressiforme and H. peltatum. Like H. peltatum, the leaf segments (pinnae) of the narrow filmy-fern are often divided on only one side. However, unlike both these species, the leaves of H. rarum do not have jagged or serrated edges.

How Ferns Are Related: Taxonomy and Evolution

The Hymenophyllaceae family is a very successful group of plants within the Pteridophytes (which includes ferns and their close relatives). This family is often called the "filmy fern family" because their leaves are so thin. There are about 670–700 named species in this family, but only about 131 are officially recognized.

The family is divided into two main groups, called genera: Hymenophyllum and Trichomanes. These two groups are separated based on how their spore cases (sori) and early life stages (gametophytes) are structured. Key differences include the shape of the indusium (the membrane covering the sorus) and the receptacle (the part that holds the sporangia).

Interestingly, the H. rarum plants found in Australia look a bit different from those in New Zealand. Australian plants have leaf segments (pinnae) that are more spread out, while New Zealand plants have pale green pinnae that overlap. Also, the sori (spore cases) of Australian H. rarum are not fully sunken into the leaf segments, and they are not limited to just the uppermost parts of the top leaves.

All members of the Hymenophyllum genus are small, thin, and delicate. They either grow on other plants (epiphytic) or on rocks, forming thick patches or mats on rainforest floors. Most plants in this family need very moist places to live. However, a few can survive dryer conditions by 'reviving' themselves when moisture becomes available again.