Asplenium L.

Terrestrial, rupestral or epiphytic ferns. Rhizomes erect or short- to long-creeping, bearing clathrate scales. Fronds monomorphic or rarely dimorphic. Laminae undivided or 1-pinnate to 4-pinnate-pinnatifid, membranous (not NZ) or herbaceous to coriaceous (NZ), usually bearing clathrate scales and sometimes hairs. Veins usually free or rarely reticulate (not NZ). Sori elongate on veins, superficial, borne on abaxial surface, usually away from margins but sometimes submarginal; paraphyses absent; indusia rarely absent, usually elongate with free ends or rarely very short or pouched, usually attached to one side of vein or rarely back to back on both sides. Sporangia brown or rarely orange-brown. Spores monolete, dark brown; perispores winged, cristate, echinate or reticulate, with plain, fenestrate, or reticulate areoles.

Aspleniaceae is dominated by the genus Asplenium, which includes over 700 species (PPG 1 2016). Numerous attempts have been made to subdivide the genus, with up to 20 segregates proposed, mainly on rather minor morphological characters, but only a few small groups have been widely recognised. Rather more convincing is the phylogenetic analysis of Schneider et al. (2004), who identified eight major clades based on rbcL and trnL-F spacer sequences amongst 71 species from throughout the world. This was enhanced by analysis of sequences from the same chloroplast regions for 21 taxa of indigenous New Zealand species (Perrie & Brownsey 2005a), and a further 21 taxa from Australia (Ohlsen et al. 2014). Both studies supported the clades originally identified by Schneider et al. (2004), and both showed that Asplenium was not monophyletic in either New Zealand or Australia. In fact, five of the eight clades of Schneider et al. (2004) are present in the two countries. Ohlsen et al. (2014) recognised a total of 13 clades, with some of the original eight clades further subdivided. In particular, Clade VII of Schneider et al. (2004) comprises several distinct subclades, two of which occur in New Zealand and are here considered separate clades (Clades IX and XI). The major clades in Asplenium have yet to be recognised in a formal taxonomic sense, and it is uncertain whether they correspond to any of the previously named segregates, except that most of the bird’s nest ferns fall into a clade that might correspond to Thamnopteris (C.Presl) C.Presl, while the northern hemisphere A. ruta-muraria L. together with species previously assigned to Pleurosorus occupy another. The majority of New Zealand and Australian species fall within Clade V of Schneider et al. (2004) along with, rather surprisingly, the bird’s nest ferns (Perrie & Brownsey 2005a; Ohlsen et al. 2014).

Allan (1961) accepted 12 species of Asplenium and one of Pleurosorus in New Zealand. Brownsey (1977b) revised the group and recognised 14 species and four subspecies of Asplenium. Subsequently a further four new species were described (Brownsey & Jackson 1984; Brownsey 1985; Brownsey & de Lange 1997; Perrie & Brownsey 2016), three subspecies were raised to species rank (Ogle 1988), and three introduced species or hybrids were identified (Brownsey in Webb et al. 1988; Heenan et al. 2004; Perrie et al. 2005). A total of 21 indigenous species and three introduced species or named hybrids is accepted here, almost doubling the number in Allan’s Flora.

In addition, Brownsey (1977a) recognised 19 different hybrids that occurred naturally in the New Zealand flora, a number that has since doubled to 37 combinations (see Hybrid combinations, Table 1). All produce abnormally formed or aborted spores and are thought to be effectively sterile. Hybrids between species of Asplenium account for more than half the total number of hybrid fern combinations recorded in New Zealand (Breitwieser et al. 2012​​​​​​​), but despite these 37 different combinations, five indigenous species (A. flabellifolium, A. pauperequitum, A. polyodon, A. subglandulosum and A. trichomanes) are not known to hybridise with any other species in New Zealand. The species that do hybridise are now known to belong to Clade V of Ohlsen et al. (2014), whereas those that do not hybridise belong to Clades III, VI, IX, and XI, reinforcing the view that the eight groupings have real phylogenetic significance.

Brownsey (1977b) showed that polyploidy had been of considerable importance in the evolution of Asplenium in New Zealand, as in other parts of the world (Kramer & Viane 1990). There are no diploids in New Zealand, and all taxa are either tetraploid (11), hexaploid (2), or octoploid (10); A. trichomanes has both tetraploid and hexaploid cytotypes, and A. flabellifolium both hexaploid and octoploid cytotypes. Evidence from morphology (Brownsey 1977b, Brownsey 1977a) and DNA sequencing (Perrie & Brownsey 2005b; Shepherd et al. 2008) strongly suggests that seven octoploid species have arisen by allopolyploidy and one by autopolyploidy, in each case with at least one of the tetraploid parents still extant in New Zealand. Some have originated more than once from the same parent species (Perrie et al. 2010).

New Zealand indigenous species are assigned to the following Clades of Ohlsen et al. (2014; also see Schneider et al. 2004; Perrie & Brownsey 2005a):

Clade III: A. subglandulosum (1 species).

Clade V: A. appendiculatum, A. bulbiferum, A. chathamense, A. cimmeriorum, A. decurrens, A. flaccidum, A. gracillimum, A. hookerianum, A. lamprophyllum, A. lepidotum, A. lyallii, A. oblongifolium, A. obtusatum, A. richardii, A. scleroprium, A. shuttleworthianum (16 species).

Clade VI: A. polyodon (1 species).

Clade IX: A. flabellifolium, A. pauperequitum (2 species).

Clade XI: A. trichomanes (1 species)

* Spore measurements are the range of mean values for sampled individuals.

Hybridism is widespread in Asplenium, with 37 different combinations listed here, based on specimens that can be identified with reasonable certainty (Table 1). In addition there is one casual hybrid, A. ×lucrosum, (Perrie et al. 2005). Plants of hybrid origin can be identified by their abnormally formed spores. Determining parentage is much more difficult and depends not only on morphology but also on field observations of what species were growing in the immediate vicinity of the putative hybrid. Even then it is virtually impossible to determine with certainty the parentage of any particular specimen.

Brownsey (1977a) listed 19 different combinations. Additional combinations have been identified subsequently as new taxa have been described (Brownsey 1983, 1985; Brownsey & de Lange 1997; Perrie & Brownsey 2004; Perrie & Brownsey 2016) and as detailed lists of taxa have been compiled for specific areas, especially offshore islands (de Lange et al. 2011; de Lange 2015). A further eight combinations are listed here for the first time. Representative voucher specimens in AK, CHR and WELT are documented for each combination.

The taxon that hybridises most frequently is A. flaccidum subsp. flaccidum, with 11 combinations, followed by A. bulbiferum and A. gracillimum with eight combinations each. By contrast, there are five indigenous species (A. flabellifolium, A. pauperequitum, A. polyodon, A. subglandulosum and A. trichomanes) that are not known to hybridise with any other species in New Zealand and that appear to be phylogenetically distinct from those that do (see Taxonomy under Asplenium).

Named hybrids:

Asplenium appendiculatum subsp. appendiculatum × richardii

= Asplenium ×canterburiense J.B.Armstr., Trans. & Proc. New Zealand Inst. 14: 361 (1882)

≡ Asplenium bulbiferum var. canterburiense (J.B.Armstr.) C.Chr., Index Fil. 104 (1905)

Holotype: Mount Arrowsmith, 4000 ft, J.F. Armstrong, March 1869, CHR 633317!

Brownsey (1977b) examined the holotype of Asplenium canterburiense and concluded that it was probably a hybrid between A. terrestre (= A. appendiculatum) and A. richardii, based on its morphology and aborted spores.

Asplenium bulbiferum × obtusatum

= Asplenium bulbiferum var. integra Kirk, Trans. & Proc. New Zealand Inst. 17: 232 (1885)

Lectotype (selected by Brownsey & Perrie 2017): Ulva [Island, Stewart Island], 14.12.1883, Herb. T. Kirk, WELT P004984 (on two sheets)!

Kirk (1885) described Asplenium bulbiferum var. integra from Ulva Island, Stewart Island. Syntype material from Kirk’s visit to Ulva in 1883 is in AK and WELT. All four sheets have fronds with aborted spores – probably derived from A. bulbiferum and A. obtusatum, but possibly involving A. gracillimum or A. scleroprium.

Cultivars: A number of cultivars of Asplenium are sold in the horticultural trade. Asplenium ×lucrosum is widely cultivated and usually sold as "Asplenium bulbiferum". Another common cultivar, "Maori Princess", may be a hybrid between A. bulbiferum and A. oblongifolium or A. obtusatum; it is possible that both combinations are present within "Maori Princess" as it is variable.

Incertae sedis

Asplenium bulbiferum var. decomposita Kirk, Trans. & Proc. New Zealand Inst. 17: 232 (1885)

Type: Ulva Island, T. Kirk [not located in AK, CHR, K, MEL, WELT]

Asplenium bulbiferum var. pseudolucidum Kirk, Trans. & Proc. New Zealand Inst. 17: 232 (1885)

Type: Ulva Island, T. Kirk [not located in AK, CHR, K, MEL, WELT]

Asplenium obtusatum var. pseudofalcatum Kirk, Trans. & Proc. New Zealand Inst. 17: 231 (1885)

Type: Mason Bay, Stewart Island, T. Kirk [not located in AK, CHR, K, MEL, WELT]

Asplenium tremulum Hombr. in Hombron & Jacquinot, Voy. Pôle Sud, Bot., Atlas t. 3b, f. Δ (1843)

≡ Asplenium bulbiferum var. tremulum (Hombr.) Domin, Biblioth. Bot. 20(85): 104 (1913)

Type: said to be from "Isles Mascaraignes, Tavaï, N’elle Zél’de" [not located in P]

The base chromosome number in Asplenium is x = 36 (Kramer & Viane 1990; Smith et al. 2006).