Classification
 Nomenclature
Scientific Name:
Asplenium pauperequitum Brownsey & P.J.Jacks., New Zealand J. Bot. 22: 315 (1984)
Synonymy:
Holotype: SE slopes of Tatua Peak, Aorangi Island, Poor Knights Islands, P.J. Jackson, 4 May 1983, WELT P11827!
Etymology:
From the Latin pauper (poor) and equites (horsemen), a reference to the Poor Knights Islands from where the species was described.
Vernacular Name(s):
Poor Knights spleenwort
 Description

Terrestrial or rupestral ferns. Rhizomes short, erect, bearing scales. Rhizome scales acicular with long filiform apices, 6–10 mm long, 0.1–0.5 mm wide, red-brown, clathrate. Fronds 40–270 mm long. Stipes 10–190 mm long, dark red-brown, shiny, bearing very narrow hair-like scales throughout. Rachises dark red-brown, scaly. Laminae 1–2-pinnate, ovate or triangular or broadly ovate, 25–100 mm long, 20–75 mm wide, glossy dark green adaxially, paler abaxially, herbaceous, almost glabrous or with occasional scales. Primary pinnae in 1–5 pairs below a broad undivided apical segment, not or only slightly overlapping, elliptic or broadly ovate; the longest at the base, 10–37 mm long, 8–32 mm wide; pinna apices obtuse or rounded, margins serrate, bases stalked or sessile. Proximal pinnae trilobed, or sometimes divided into a pair of secondary pinnae; the latter elliptic, 10–20 mm long, 7–14 mm wide, apices obtuse, margins serrate, bases stalked. Sori away from margins; indusia 4–12 mm long, curved away from midribs; free margins of indusia entire. Mean spore size 49–54 μm long, 34–38 μm wide; perispores with reticulate, flattened projections.

 Recognition

Asplenium pauperequitum is readily distinguished from most New Zealand species by its thin, shiny, red-brown stipe and rachis. All other species, except A. trichomanes, A. polyodon, and the naturalised A. aethiopicum, have stipes and rachises that are green at least in the distal part. Asplenium pauperequitum is distinguished by its primary pinnae, which are either trilobed or divided into a single pair of secondary pinnae, whereas in A. trichomanes and A. polyodon the fronds are 1‑pinnate with many more pairs of pinnae. In A. aethiopicum the laminae are at least 2-pinnate and also have many more pairs of pinnae.

 Distribution

Northland.

Chatham Islands.

Altitudinal range: 0–190 m.

Asplenium pauperequitum is currently known only from Tawhiti Rahi and Aorangi  Islands in the Poor Knights group (Brownsey & Jackson 1984), from north-west Chatham Island (AK 295186, WELT P021515), and from the Forty Fours, Chatham Islands (Cameron et al. 2006). It apparently formerly occurred on the Mokohīnau Islands, where it was collected in the 1880s by the lighthouse keeper, F.S. Sandager (AK 135800), but has not been seen there since (Cameron 1993). It occurs from sea level on Chatham Island to 190 m on Aorangi Island.

 Habitat

Asplenium pauperequitum is a rupestral species that grows in seepages and crevices, and on damp surfaces of rhyolitic rock on the Poor Knights Islands, either on exposed bluffs or under a coastal forest canopy of Metrosideros excelsa. On Chatham Island it was recorded growing under a schist overhang, and on the Forty Fours it grew in a deep rock crevice near the summit of the island (Cameron et al. 2006). Plants are often associated with guano or seabird roosts and nest. The species appears to be naturally prone to major population fluctuations (de Lange et al. 2010).

 Biostatus
Indigenous (Endemic)

Asplenium pauperequitum was given a conservation status of Nationally Endangered by de Lange et al. (2013).

 Hybridisation

Asplenium pauperequitum is unusual among New Zealand species of the genus in that it has not been recorded hybridising with any other species. Its isolated phylogenetic position in Clade IX of Ohlsen et al. (2014), in contrast to most New Zealand species, which occur in Clade V, may account for this.

 Cytology

n = c. 144 (Brownsey & Jackson 1984).

 Notes

There is a remarkable disjunction between the populations of A. pauperequitum on the Poor Knights Islands and those on the Chatham Islands, which may be due to dispersal of spores by seabirds (Cameron et al. 2006).

 Bibliography
Brownsey, P.J.; Jackson, P.J. 1984: Asplenium pauperequitum - a new fern species from the Poor Knights Islands, New Zealand. New Zealand Journal of Botany 22(2): 315–321.
Brownsey, P.J.; Perrie, L.R. 2018: Aspleniaceae. In: Breitwieser, I.; Wilton, A.D. (ed.) Flora of New Zealand — Ferns and Lycophytes. Fascicle 18. Manaaki Whenua Press, Lincoln.
Cameron, E.K. 1993: Asplenium pauperequitum – a new locality. New Zealand Botanical Society Newsletter 34: 7–8.
Cameron, E.K.; de Lange, P.J.; Perrie, L.R.; Brownsey, P.J.; Campbell, H.J.; Taylor, G.A.; Given, D.R.; Bellingham, R.M. 2006: A new location for the Poor Knights spleenwort (Asplenium pauperequitum, Aspleniaceae) on The Forty Fours, Chatham Islands, New Zealand. New Zealand Journal of Botany 44: 199–209.
de Lange, P.J.; Heenan, P.B.; Norton, D.A.; Rolfe, J.R.; Sawyer, J. 2010: Threatened plants of New Zealand. Canterbury University Press, Christchurch.
de Lange, P.J.; Norton, D.A.; Courtney, S.P.; Heenan, P.B.; Barkla, J.W.; Cameron, E.K.; Hitchmough, R.; Townsend, A.J. 2009: Threatened and uncommon plants of New Zealand (2008 revision). New Zealand Journal of Botany 47: 61–96. [Nationally Endangered]
de Lange, P.J.; Norton, D.A.; Heenan, P.B.; Courtney, S.P.; Molloy, B.P.J.; Ogle, C.C.; Rance, B.D. 2004: Threatened and uncommon plants of New Zealand. New Zealand Journal of Botany 42(1): 45–76.
de Lange, P.J.; Rolfe, J.R.; Barkla J.W.; Courtney, S.P.; Champion, P.D.; Perrie, L.R.; Beadel, S.N.; Ford, K.A.; Breitwieser, I.; Schönberger, I.; Hindmarsh-Walls, R.; Heenan, P.B.; Ladley, K. 2018: Conservation status of New Zealand indigenous vascular plants, 2017. New Zealand Threat Classification Series No. 22. [Nationally Endangered]
de Lange, P.J.; Rolfe, J.R.; Champion, P.D.; Courtney, S.P.; Heenan, P.B.; Barkla, J.W.; Cameron, E.K.; Norton, D.A.; Hitchmough, R.A. 2013: Conservation status of New Zealand indigenous vascular plants, 2012. New Zealand Threat Classification Series 3. Department of Conservation, Wellington. [Nationally Endangered]
Ohlsen, D.J.; Perrie, L.R.; Shepherd, L.D.; Brownsey, P.J.; Bayly, M.J. 2014: Phylogeny of the fern family Aspleniaceae in Australasia and the south-west Pacific. Australian Systematic Botany 27: 355–371.