The maidenhair spleenwort is a spleenwort fern (Asplenium) that (supposedly) looks like a maidenhair fern (Adiantum, see below). The 600 or so of the world’s spleenworts are characterised by having their reproductive structures in lines away from the margins of their fronds’ undersides.
Two maidenhair spleenworts occur in New Zealand. They look very similar, but one has four sets of chromosomes (tetraploid) and the other six (hexaploid). This difference in chromosome number means they cannot interbreed. In New Zealand, the hexaploid is common, but the tetraploid is rare, only being known from the Hawke’s Bay, and only recently being rediscovered. Outside New Zealand, the hexaploid is rare, being known from only a few places in Australia, while the tetraploid is common and widespread around the world.
Maidenhair spleenworts are most commonly found on limestone rock. They can be out in the open, or under semi-shade, but usually in fairly dry conditions. They often hold their fronds erect, whereas other ferns growing from rock usually have pendulous fronds.
The taxonomy of New Zealand’s maidenhair spleenworts is still being researched. The tetraploid may be referable to Asplenium trichomanes subsp. quadrivalens. The correct scientific name for the hexaploid, the most common maidenhair spleenwort in New Zealand, is presently unclear.
Maidenhair spleenworts can be distinguished from other New Zealand ferns by the combination of their typical spleenwort reproductive structures (see above), and their frond stems which are almost black, almost smooth (without hairs and with only a few scales), and undivided (i.e., the stems do not branch). Similar-looking ferns in New Zealand are described below.
Necklace fern, Asplenium flabellifolium.
A spleenwort or Asplenium fern like the maidenhair spleenworts can be most obviously distinguished from the maidenhair spleenworts by its green stem.
The maidenhairs are most obviously distinguished from the maidenhair spleenworts by the branching stems of their fronds. The Small maidenhair (Adiantum diaphanum) can sometimes have unbranched frond stems, but it, like all maidenhairs, can be reliably distinguished by having the reproductive structures on the margins of their fronds’ undersides.
Button fern, Pellaea rotundifolia.
The brown and scaly frond stems and reproductive structures on the margins of their fronds’ undersides distinguish button ferns from the maidenhair spleenworts.
Like most Blechnum ferns, Creek fern (Blechnum fluviatile) and Lance fern (Blechnum chambersii) have very different looking fertile and sterile fronds. Those fronds that are making spores have much narrower segments, are held more erect, and are black or brown (they are not dead despite their lack of greenness!).
We are still interested in learning more about the maidenhair spleenworts in the southern North Island (south of, and not including, the Waikato). I would be very grateful for notification (and a photo) if you think you have found maidenhair spleenwort in the southern North Island. Please either email (firstname.lastname@example.org), phone (04 381 7261), or write me (Leon Perrie, Te Papa, PO Box 467, Wellington).