Pakau

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 61-62

PAKAU

Pakau S.E. Fawc. & A.R. Sm. , gen. nov.

— TYPE: Pakau pennigera (G.Forst.) S.E. Fawc.& A.R.Sm. [= Polypodium pennigerum G. Forst., Fl.Ins. Austr.Prodr. 82.1786.]

For complete species synonymy see Brownsey et al.(1985).

Etymology.— Pākau , or pākauroharoha, is the common name for this fern in the Māori language. The word may also refer to wing (Moorfield 2019), similar to the dual meanings of the Greek word pteris (fern or feather).

Plants large and terrestrial, from <0.5 m to> 2.5 m in height; rhizomes sometimes forming massive erect caudices to 1 m tall, or decumbent; fronds monomorphic, pinnate-pinnatifid, arching; stipes light brown, with brown ovate to lanceolate glabrous scales on stipe bases; blades membranaceous to chartaceous, drying dull green, ovate to lanceolate; two to five pairs of proximal pinnae gradually reduced, the lowest 1–4(–6) cm long (never rudimentary or glanduliform); pinnae opposite or subopposite ( Fig. 7F ), even towards blade apex, grooved adaxially, (10–)15–30 pairs, lobes oblique, rounded with crenulate margins, incised halfway or a little more to costae, proximal pinnae frequently auricled, with acroscopic auricles often secondarily lobed; costules 5–7 mm apart; veins commonly about 6–9 pairs per segment, prominent both adaxially and abaxially, generally with one pair anastomosing below cartilaginous sinuses (sometimes forming a whitish, protruding apophysis to 0.5 mm long abaxially), and a second vein pair running to the sinus; aerophores absent; indument abaxially of brown, often lustrous, ovate to deltate scales (to 1 mm wide and about as long) along rachis and costae ( Fig. 7E ), hairs sparse and short, unicellular, acicular or capitate on costae, or lacking; indument adaxially of arching reddish brown hairs on rachis and costae, the hairs directed toward pinna and blade tips, short sparse capitate or acicular hairs present on costae, generally lacking on secondary veins and laminae; pustules absent; sori inframedial, exindusiate, the basal pair or two on each segment (larger fronds) often oval, to twice as long as wide ( Fig. 7E ); sporangia unadorned, each with a short stalk ca. 1/4–1/2 the capsule length; spores black, with small, irregular wings; x = 36, 2 n = 144 (only tetraploids known).

Diagnosis.— Pakau may be easily distinguished from Christella and Macrothelypteris by its essentially glabrous laminae, and from Cyclosorus interruptus by its erect or decumbent rhizomes (vs. long-creeping). Pakau differs from other segregates of Pneumatopteris in having persistent ovate to deltate scales on the abaxial costae, lack of aerophores at pinna bases, non-pustular laminae, laminae with proximal pinnae gradually reduced but lacking rudimentary pinnae, and black spores.Another distinctive feature of Pakau is its opposite pinnae; although some other Thelypteridaceae have opposite or subopposite proximal pinnae, these usually transition to an alternate arrangement towards the frond apex. The lobing of the acroscopic auricles on the pinna bases is also characteristic and unusual within the family (but see Pelazoneuron patens , and some Christella spp. ). Holttum (1971:43) thought Pneumatopteris pennigera was possibly related to a species that we here treat as Menisorus , Goniopteris madagascariensis Fée (= Pneumatopteris unita (Kunze) Holttum ), from Africa ( Holttum 1974a). Molecular evidence (Fawcett et al. in press) suggests the two species diverged successively from the backbone of the phylogeny and are on long branches ( Fig. 1 ).

Biogeography and ecology. —This monotypic genus is restricted to New Zealand, southeastern Australia, and Tasmania ( Brownsey & Perrie 2016). Pakau pennigera is a plant of lowland (<800 m), relatively undisturbed rain forests, especially of dark, heavily shaded gullies. It stands apart from other genera in the family in having a strictly austral distribution, but it does not extend to frost-prone latitudes. Fossil evidence suggests that Pakau , or its close relatives, were present in New Zealand at least since the early Miocene ( Pole 1992).

Taxonomic and phylogenetic studies.— Pakau has been treated most recently in the genus Pneumatopteris ( Holttum 1971, 1973a, 1974a, 1977b; Brownsey & Smith-Dodsworth 1989: fig. 112 A-B; Bostock 1998: fig. 121F-G), but even with this placement, Holttum realized that this species was somewhat apart from other Pneumatopteris in the exindusiate sori, presence of costal scales, and absence of rudimentary proximal pinnae. The highly polyphyletic genus Pneumatopteris is recircumscribed in the present work; see the Pneumatopteris treatment for further details. Based on recent molecular phylogenetic evidence (Fawcett et al. in press), Pakau is quite distinct from any extant genus of Thelypteridaceae ; it resolves on a long branch, sister to the rest of the christelloid clade, which is a subclade of the cyclosoroid genera (including Christella , Plesioneuron , Pneumatopteris , Pronephrium , Pseudocyclosorus , and Sphaerostephanos ) all sensu Holttum (1971), as well as a half dozen smaller genera ( Fig. 1 ). The christelloid genera are almost exclusively Old World, primarily restricted to southeastern and southern Asia, Malesia, Melanesia, and Polynesia, with the exception of the three earliest-diverging lineages: The New Zealand and Australian Pakau , African Menisorus , and neotropical/subtropical Pelazoneuron .

Figures

FIG.7.A.Pneumatopteris parksii,Fawcett 645 (UC),pinna lobes,adaxial view.B.Reholttumia magnifica,Fawcett 676 (VT),pinna lobes,abaxial view.C.Pelazoneuron patens,Fawcett 744 (VT), abaxial pinna-lobes.D. P.serra,Fawcett 1034 (VT), adaxial pinna lobes.E. Pakau pennigera, Given 11842 (VT),pinna lobes,abaxial view. F.Pakau pennigera, Stuart s.n.(VT),pinna.

FIG. 1. A synoptical treeillustrating relationships among genera of Thelypteridaceae based on Fawcett et al.(in press).