Scientific Name:
Adiantum L., Sp. Pl. 1094 (1753)
From the Greek adiantos (unwettable), a reference to the water-shedding properties of the lamina.
Vernacular Name(s):
huruhuru tapairu; maidenhair fern; tawatawa

Terrestrial or rupestral ferns. Rhizomes erect to long-creeping, scaly; roots rarely bearing small tubers. Rhizome scales non-clathrate, acicular to narrowly ovate or narrowly triangular, attached at base, concolorous, yellow-brown to red-brown or dark brown. Fronds monomorphic. Stipes and rachises red- or dark brown, highly polished. Laminae 1–5-pinnate or rarely helicoid, herbaceous or coriaceous, glabrous or hairy or rarely scaly (not NZ), rarely glaucous or farinose (not NZ) abaxially. Pinnae not articulated to rachis; ultimate segments rarely articulated to costae and deciduous (not NZ). Veins free or rarely reticulate (not NZ). Sori borne mainly on acroscopic margins of lamina segments, on the underside of orbicular to elongate, modified, reflexed, marginal, lamina flaps (“indusia”); paraphyses absent or rarely present (not NZ). Spores trilete, lacking chlorophyll; perispores scabrate, rugose or tuberculate, without an equatorial flange.


A genus of c. 225 species, included in the subfamily Vittarioideae (PPG 1 2016).

Adiantum is now considered to be monophyletic and sister to the vittarioid ferns (Pryer et al. 2016), although this relationship was regarded as uncertain (e.g. Bouma et al. 2010) until adequate taxon sampling had been achieved. Even now, there is insufficient sampling across the whole genus to determine how many clades are present. Bouma et al. (2010) were able to identify three major clades, with all of the indigenous New Zealand species present in clade C along with other species from different southern hemisphere continents. However, their sampling outside New Zealand was very limited. Lu et al. (2011) sampled 86 taxa from a wider geographical range using five plastid markers and found nine major clades, six of them within Chinese Adiantum. Nevertheless, the phylogeny of the genus as a whole still requires further investigation. Tryon & Tryon (1982) recognised eight major groups on morphological grounds, but there has been no modern monograph of the genus.

Within New Zealand, Allan (1961) recognised six indigenous species – A. aethiopicum, A. cunninghamii, A. diaphanum, A. formosum, A. fulvum and A. hispidulum. Parris & Croxall (1974) subsequently reinstated A. viridescens, Parris (1980) suggested that A. pubescens should be recognised in addition to A. hispidulum, and Brownsey (in Webb et al. 1988) added two naturalised species to the New Zealand flora. However, Large & Braggins (1993) found that A. hispidulum and A. pubescens could only be distinguished on the basis of their hair characters, and even then with a high degree of variability. They treated A. pubescens as a variety of A. hispidulum. Brownsey et al. (2019) investigated the presence or absence of hairs on the abaxial lamina surfaces of all indigenous New Zealand Adiantum species, and concluded that most are dimorphic in this regard, and that such variation should be treated as variation within the bounds of individual species distinguished on the basis of other morphological characters, a conclusion also reached for Australian and Malesian plants by Bostock (1992). As a consequence, Brownsey et al. (2019) reduced A. viridescens to synonymy with A. fulvum.

Species of Adiantum are widely cultivated throughout the world. Many of the cultivars and species in cultivation have been described and illustrated by Goudey (1985) and Hoshizaki & Moran (2001).

1Ultimate lamina segments flabellate, stalk attached centrally2
Ultimate lamina segments ± oblong, stalk attached at one corner4
2Reflexed lamina segments (“indusia”) oblong, lacking a sinuscapillus-veneris
Reflexed lamina segments (“indusia”) reniform, each with a distinct sinus3
3Ultimate lamina segments generally broader than long, usually undivided, notched only at point of attachment of the “indusia”, or rarely incised to the depth of the indusial notchesaethiopicum
Ultimate lamina segments generally longer than broad, with at least some incised more deeply than the indusial notches, divided into two or more distinct lobesraddianum
4Reflexed lamina segments (“indusia”) hairy5
Reflexed lamina segments (“indusia”) glabrous6
5Laminae 1–2-pinnate, with secondary pinnae, where present, only on the proximal pair of primary pinnae; rachis glabrousdiaphanum
Laminae 3-pinnate or helicoid with the rachis repeatedly dividing pseudo-dichotomously; rachis hairyhispidulum
6Costae of primary pinnae glabrous7
Costae of primary pinnae hairy8
7Laminae 1–2-pinnate, with secondary pinnae, where present, only on the proximal pair of primary pinnae; rhizome erect, rootlets often bearing small tubersdiaphanum
Laminae 2–4-pinnate at base, usually with more than one pair of divided primary pinnae; rhizome creeping, rootlets lacking tuberscunninghamii
8Laminae usually 4-pinnate at base (rarely 3- or 5-pinnate); stipes rough but glabrous; ultimate lamina segments ± oblong, up to 16 mm longformosum
Laminae usually 3-pinnate at base (rarely 2- or 4-pinnate); stipes scaly proximally and bearing antrorse hairs distally; ultimate lamina segments often curved acroscopically at apices, up to 26 mm longfulvum

In New Zealand, species of Adiantum can be recognised by their 1–5-pinnate fronds, polished dark brown stipes, flabellate or oblong ultimate lamina segments, and sori protected by reflexed lamina segments that are usually reniform or sometimes oblong. The spores are trilete and scabrate (Large & Braggins 1991).


Adiantum is pantropical in distribution, with a few species also extending to both the north and south temperate regions. Many species have become naturalised in different parts of the world. The greatest diversity is in the Neotropics, where more than half the species are found (Mickel & Smith 2004); six indigenous and one naturalised species in southern Africa (Crouch et al. 2011), eight in Australia (Bostock 1998), ten indigenous and two naturalised in the south-west Pacific (Nakamura 2008), and one indigenous and four naturalised in Hawai‘i (Palmer 2003). Eight species in New Zealand; two endemic, four indigenous, and two naturalised.

Indigenous (Non-endemic)
Number of species in New Zealand within Adiantum L.
Indigenous (Endemic)2
Indigenous (Non-endemic)4
Exotic: Fully Naturalised2

The base chromosome number in Adiantum is x = 29 or 30, but there is also at least one aneuploid with x = 57 and an extensive polyploid series with diploids through to decaploids recorded (Tryon 1990; Tindale & Roy 2002).

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