Tangle ferns untangled

A focus for my research in 2014 has been preparing an account on the Gleicheniaceae fern family for the online Flora of New Zealand.

More on the revolutionary online Flora of New Zealand.

Carrier tangle, matua-rarauhe, Gleichenia microphylla. Tangle ferns have fronds that repeatedly divide in two. These branches get entangled with one another and with other vegetation. Hence their common name of “tangle ferns”. Photo: Leon Perrie. © Te Papa.

Carrier tangle, matua-rarauhe, Gleichenia microphylla. Tangle ferns have fronds that repeatedly divide in two. These branches get entangled with one another and with other vegetation. Hence their colloquial name of “tangle ferns”. Photo: Leon Perrie. © Te Papa.

The Gleicheniaceae in New Zealand comprises nine species in the genera Dicranopteris (one species, restricted to central North Island thermal areas), Gleichenia (four species), and Sticherus (four species).

It is the Gleichenia tangle ferns that have required the most study. Determining their taxonomy – how many species are present, and what are their scientific names? – has been as complicated as their entangling fronds. But I think I’ve made some progress, which I’d like to share.

Tangle ferns made simple

The undersides of the four species of Gleichenia tangle fern accepted for New Zealand. From top: alpine tangle fern, Gleichenia alpina; tangle fern, waewae-kötuku, Gleichenia dicarpa; pitted tangle fern, Gleichenia inclusisora; carrier tangle, matua-rarauhe, Gleichenia microphylla. Scale bar = 2 cm. Composite image © Te Papa.

The undersides of the four species of Gleichenia tangle fern accepted for New Zealand. From top: (1) alpine tangle fern, Gleichenia alpina; (2)  tangle fern, waewae-kōtuku, Gleichenia dicarpa; (3) pitted tangle fern, Gleichenia inclusisora; (4) carrier tangle, matua-rarauhe, Gleichenia microphylla. Scale bar = 2 mm. Composite image © Te Papa.

When viewed from above, the tangle ferns in New Zealand look fairly similar to one another. (The exception is Gleichenia alpina, which has shorter branches.) But if you turn them over and look closely, you’ll see some marked differences.

Indeed, they are so different that you might be wondering what the trouble was…

Te Papa’s collections of Gleichenia tangle ferns, with maps and more pictures.

Extra for experts

The problem is that some plants do not match the four pictured above. There are at least two reasons.

The first is that plants that have intermediate characteristics or combine the characteristics of Gleichenia dicarpa and Gleichenia microphylla are common.

As background, Gleichenia microphylla has green undersides to its frond segments, ultimate segments that are flat or recurved (but not pouched) and often have pointed apices, and spore capsules (sporangia) that occur in clusters of three or more. In contrast, Gleichenia dicarpa has white undersides to its frond segments, ultimate segments that are pouched or recurved with rounded apices, and spore capsules (sporangia) usually in clusters of only two. They also have different kinds of scales (the appendages that occur on the axes, and which are wider than hairs).

But plants with more or less flat ultimate segments that are whitish underneath also occur (as do some other combinations of characteristics). It is likely that these ‘intermediate’ plants are hybrids. But I have no independent proof of this.

The second reason is that there are (at least) two distinct morphologies in Gleichenia dicarpa.

The undersides of four plants of Gleichenia dicarpa. The pertinent difference is that the appendages – “scales”, being wider than hairs – do not extend along the length of the axis. This is the most common and widespread morphology. In the other three pictured plants, there are scales extending along the length of the axis. Scale bar = 2 cm. Composite image © Te Papa.

The undersides of four plants of Gleichenia dicarpa. The pertinent difference is that the appendages – “scales”, being wider than hairs – do not extend along the length of the axis in the plant second-from-top. This is the most common and widespread morphology. In the other three pictured plants, there are scales extending along the length of the axis. Scale bar = 2 mm. Composite image © Te Papa.

In some plants of Gleichenia dicarpa, scales occur along the full length of the underside of the minor axes (technically, on the abaxial surface of the alpha costae). These plants also have minute scales on the underside of the frond segments (technically, on the abaxial surface of the ultimate segments). Such plants are dominant in the northern North Island, and also occur in the southern and eastern South Island, Stewart Island, and on the Chatham Islands, and they are scattered elsewhere in the North and South Islands. Interestingly, these plants are genetically heterogeneous.

But in most New Zealand plants of Gleichenia dicarpa, the scales on the underside of the minor axes (i.e., on the abaxial surface of the alpha costae) do not extend along the full length of the minor axes. And, there are no scales on the underside of the frond segments (i.e., the abaxial surface of the ultimate segments is glabrous).

So, not so simple…

How you can help

I am not sure what this means for Gleichenia dicarpa.  But, I am very interested in observations or specimens of Gleichenia dicarpa from either

  • south of Auckland that have scales occurring along the length of the underside of the minor axes; or
  • north of Auckland that lack scales along the length of the underside of the minor axes.

Photos uploaded to the Ferns with Te Papa project in NatureWatch would be gratefully appreciated. And your photo might end up in the exhibition DeCLASSIFIED! Nature’s secrets exposed at Te Papa.

The Ferns with Te Papa project in the citizen science website NatureWatch NZ.

More on the exhibition DeCLASSIFIED! Nature’s secrets exposed at Te Papa.

Email me.

The online Flora of New Zealand

Are you interested in expert accounts of New Zealand’s plants? Then the Flora of New Zealand is for you!

The online Flora of New Zealand – what is it?

Our treatment for the Gleicheniaceae is still in preparation. However, ten fern families are online. Five of these have downloadable pdfs. More are scheduled for release in February 2015.

pdf for the Osmundaceae, as an example of what is being prepared.

List of all of the treatments currently available as pdfs.

Previous posts on Gleichenia and Sticherus

I’ve posted before about our work on the Sticherus umbrella ferns and a new species of Gleichenia tangle fern.

Blog post about the recently discovered Gleichenia inclusisora.

Blog post about recent work with Sticherus.

4 Responses

  1. Patricia Hendy

    A very informative read What about the silver fern. I fell in love with silver fern I found growing in Arkles Bay.

    Reply
  2. Michael Sundue

    Great photos! I use these to revise the material in our herbarium and see what we have.

    Reply
    • Leon Perrie

      Thanks Michael. I’ve been inspired by the recent book “Ferns of Southern Africa” by Crouch et al. They use tables (with words) to distinguish similar species. Very useful/accessible, I think. I’m wondering about taking that approach further with pictures of the diagnostic characteristics.

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