Classification
 Nomenclature
Scientific Name:
Adiantum formosum R.Br., Prodr. Fl. Nov. Holland. 155 (1810)
Synonymy:
Lectotype (selected by Field 2020): Port Jackson [Sydney, Australia], R. Brown Iter Austral. 67, 1802-5, BM 001044143!
Etymology:
From the Latin formosus (handsome, beautiful), a reference to the perceived appearance of this species.
Vernacular Name(s):
giant maidenhair; plumed maidenhair
 Description

Rhizomes long-creeping, up to 135 mm long (in herbarium specimens), 3–6 mm diameter, with stipes widely inserted; bearing scales; stolons and tubers absent. Rhizome scales narrowly ovate, 0.8–2 mm long, 0.1–0.3 mm wide, red-brown, appressed, concolorous. Fronds 470–970 mm long. Stipes 250–660 mm long, dark brown, tuberculate, rough, scattered scales proximally. Rachises dark brown, sulcate, sparsely tuberculate, slightly rough. Laminae usually 4-pinnate, or rarely 3-pinnate or 5-pinnate, broadly ovate, 200–450 mm long, 180–430 mm wide, dark green on both surfaces, herbaceous, glabrous on adaxial surface, glabrous or bearing pale flattened hairs on abaxial surface. 7–11 pairs of divided primary pinnae below long pinnate apex, overlapping, ovate or broadly ovate; costae bearing antrorse red-brown hairs; the longest pinnae at or near the base, 140–360 mm long, 110–320 mm wide, apices acute to acuminate, bases stalked, divided into secondary pinnae. 6–9 pairs of secondary pinnae on the proximal primary pinnae divided into tertiary pinnae; the longest secondary pinnae ovate or narrowly ovate, 75–220 mm long, 24–110 mm wide, apices acute to acuminate, bases stalked, divided into tertiary or quaternary pinnae, or rarely even more divided. Longest ultimate lamina segments oblong, 9–16 mm long, 4–8 mm wide, apices obtuse, acroscopic margins lobed or toothed, basiscopic margins ± entire, bases stalked, with stalks attached in one corner. Reflexed lamina flaps lunulate, glabrous.

 Recognition

Adiantum formosum is the largest and most divided of the indigenous species in New Zealand. It is usually 4-pinnate at the base but small fronds may occasionally be 3-pinnate and large fronds rarely 5-pinnate. It has oblong ultimate segments with the stalk attached in one corner, rough but glabrous stipes and rachises, hairy costae on the pinnae, lunulate and glabrous “indusia”, and a green abaxial lamina surface. Plants from Northland (now believed extinct) have pale hairs on the abaxial lamina surfaces, but those from the Manawatū are glabrous.

 Distribution

North Island: Northland, Auckland, Southern North Island

Altitudinal range: 50–90 m.

Adiantum formosum is currently found only in lowland sites around the Manawatū Gorge. It was formerly collected from the Wairoa River and Kaipara Harbour in Northland, but is now thought to be extinct in that region. Collections from Whangārei need confirmation, possibly having come from cultivated plants, or labelled with a broad and imprecise locality, and they are not mapped here. There are no collections in AK, CHR or WELT to substantiate records from Reef Point and Herekino (Crookes 1963; Bartlett 1980), and they must be regarded as suspect. The species is easily cultivated and it is unclear whether populations adjacent to the Manawatū Gorge, at Linton, Lake Horowhenua and in native forest at Masterton, are natural or the result of plantings, and they are not mapped here. Populations in Auckland city, Titirangi, Waitākere, Pukekohe and Pukekura Park are definitely cultivated.

Also Australia (Queensland, New South Wales, Victoria). Naturalised in Sri Lanka (Fraser-Jenkins et al. 2017).

 Habitat

In the vicinity of the Manawatū Gorge, Adiantum formosum grows on river terraces and streambanks under podocarp/broadleaved forest and scrub. It also occurs under pines and willows.

 Biostatus
Indigenous (Non-endemic)

Adiantum formosum was given a conservation status of At Risk – Relict by de Lange et al. (2018).

 Cytology

n = 58 (Brownlie 1961).

 Notes

Adiantum formosum in Australia is dimorphic with respect to hairs on the abaxial lamina surfaces – some populations are glabrous, others bear pale, flattened hairs. The fact that, in New Zealand, plants from Northland are hairy but those from elsewhere are glabrous suggests these populations have resulted from at least two different dispersal events. The two forms have not been given any taxonomic recognition in Australia (Bostock 1998) and are treated here as dimorphic character states within A. formosum (Brownsey et al. 2019).

 Bibliography
Bartlett, J.K. 1980: New and significant plant distribution records from northern New Zealand. New Zealand Journal of Botany 18: 347–351.
Bostock, P.D. 1998: Adiantaceae. In: Flora of Australia. Vol. 48. 248–269.
Brown, R. 1810: Prodromus Florae Novae Hollandiae et Insulae Van-Diemen. Johnson, London.
Brownlie, G. 1961: Additional chromosome numbers – New Zealand ferns. Transactions of the Royal Society of New Zealand. Botany 1: 1–4.
Brownsey, P.J.; Given, D.R.; Lovis, J.D. 1985: A revised classification of New Zealand pteridophytes with a synonymic checklist of species. New Zealand Journal of Botany 23(3): 431–489.
Brownsey, P.J.; Perrie, L.R. 2021: Pteridaceae. In: Breitwieser, I. (ed.) Flora of New Zealand — Ferns and Lycophytes. Fascicle 30. Manaaki Whenua Press, Lincoln.
Brownsey, P.J.; Shepherd, L.D.; Perrie, L.R. 2019: A consistent taxonomic treatment for dimorphic variation in New Zealand Adiantum species. New Zealand Journal of Botany 57(4): 249–260.
Brownsey, P.J.; Smith-Dodsworth, J.C. 2000: New Zealand ferns and allied plants. Edition 2. David Bateman, Auckland.
Crookes, M.W. 1963: New Zealand Ferns, ed. 6. Incorporating illustrations and original work by H.B. Dobbie. Whitcombe & Tombs, 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. [Relic]
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. [Relic]
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. [Relic]
Field, A.R. 2020: Classification and typification of Australian lycophytes and ferns based on Pteridophyte Phylogeny Group classification PPG 1. Australian Systematic Botany 33: 1–102.
Fraser-Jenkins, C.R.; Gandhi, K.N.; Kholia, B.S.; Benniamin, A. 2017: An annotated checklist of Indian Pteridophytes. Part 1. Lycopodiaceae to Thelypteridaceae. Bishen Singh Mahendra Pal Singh, Dehra Dun, India.