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Plant of the week: Lobed Maidenhair Spleenwort

Entry number #2 in our Plant of the Week series is the elusive Lobed Maidenhair Spleenwort

In contrast to our last Plant of the Week, this week’s species is by all accounts a little less showy. That said, like the Lindisfarne Helleborine, this is an extremely rare plant that thanks to an unexpected trip to Hareshaw Linn in Northumberland, I recently had the chance to see for the first time.

Lobed Maidenhair Spleenwort, Asplenium trichomanes subsp. pachyrachis

Many of us are familiar with with Maidenhair Spleenwort (Asplenium trichomanes), the delicate, trailing fern adorning garden walls and other structures throughout our towns and cities. What you may not know, however, is that the UK is home to several subspecies of this lovely little fern, one of which is the Lobed Maidenhair Spleenwort (Asplenium trichomanes subsp. pachyrachis).

This unassuming fern grows on calcareous rocks such as limestone in shaded, humid settings. Often under rock overhangs, on steep valley sides or beside waterfalls, such as at Hareshaw Linn. Unlike it’s more familiar cousins, it is seldom found on mortared walls and is unlikely to crop up in towns.

A genuinely rare subspecies in the UK, Lobed Maidenhair Spleenwort is found at only a scattering of sites. A notable concentration can be found in south Wales, with a further cluster of records near Chester. Elsewhere, it is found sporadically in small populations at isolated sites. This fern is widespread in Southern Europe, particularly in Spain, France and Italy, so may well be under-recorded in the UK.

The specific epithet trichomanes refers to a Greek word for fern

What does it look like?

Lobed Maidenhair Spleenwort is a small, tufted plant that often appears to grow flat against the surface of rock. Its narrow, green fronds are usually 5-30mm long and contain at their centre a dark, glossy mid-rib – a useful feature for seperating this group from Green Spleenwort (Asplenium viride). The pinnae or leaflets usually number in at 20-30 pairs and are arranged oppositely along the frond. All of this, however, appeals to other Maidenhair Spleenworts too, so what sets this subspecies apart?

The main difference between Lobed Maidenhair Spleenwort and other subspecies is the margin of pinnae. As its name suggests, those of this fern are distinctly lobed, almost scalloped. In contrast, those of other subspecies may be asymmetrical or rectangular but only slightly toothed. It may only be an anecdotal observation, but I think the lobes give the leaflets of this fern an arrow-like shape…

Given it’s similarities to other Miadenhair Spleenworts, it is little wonder this fern is poorly recorded. Sure, it may be rare, but it must be present unoticed at further sites. Will you find it?

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