Hoiokula, S.E. Fawc. & A.R. Sm., S. E. Fawc. & A. R. Sm.

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 48-49

HOIOKULA

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

— TYPE: Hoiokula sandwicensis (Brack.) S.E. Fawc. & A.R. Sm. [= Stegnogramma sandwicensis Brack.,U.S.Expl.Exped.,Filic. 16:26.1854.]

Etymology.—Ho’i’o kula is the common name for H. sandwicensis in the native Hawaiian language ( Palmer 2003), and it is valued for its edible fiddleheads ( Pukui & Elbert 2003).

Plants terrestrial, cremnophilous or rheophytic, from 40 cm to> 1 m tall; rhizomes short-creeping; fronds once-pinnate, monomorphic, erect ( H. sandwicensis ) or pendent ( H. pendens ); stipes stramineous or dull brown, stipe bases and rhizome scales dull brown, glabrous or with short surficial hairs, ovate to linear-lanceolate; blades chartaceous, drying green, lanceolate to broadly deltate, apex gradually reduced, with distal pinnae somewhat decurrent, proximal pinnae not or only slightly reduced, basal pair sometimes somewhat deflexed, proliferous buds absent; pinnae crenate, dentate, shallowly lobed (<halfway to costae), or subentire, typically straight, less commonly falcate, with acroscopic auricles, grooved adaxially; veins prominent abaxially and adaxially, anastomosing with several pairs uniting below the sinus into a zig-zag excurrent vein, veins ending at pinna margins; aerophores absent, or a small patch of darkened aerating tissue, sometimes slightly swollen or tuberculate; indument abaxially of broad-based (stout), tapering hyaline acicular hairs on veins and between veins, or restricted to veins, indument adaxially of hyaline acicular hairs on and between veins, hairs on stipes and rachises short (<1 mm) and sparse ( H. sandwicensis ), or long (> 1 mm) and abundant ( H. pendens , Fig. 4B ), single-celled or septate; glands usually absent, but when present, spherical, translucent yellow-orange, on laminae, veins, and sporangia; pustules absent on laminar tissue; sori medial, round or elongate along veins, exindusiate; sporangia abundantly to sparsely setulose ( Fig. 2H ), rarely glabrous; spores pale brown, with broad wings, in H. sandwicensis with secondary sculpturing of fimbriate microstructure ( Tryon & Lugardon 1991). Ploidy and hybrids are unknown, but the basic chromosome number is likely to be x = 36, as is the case for its closest relatives.

Diagnosis. —In Hawaii, Hoiokula is distinguished from Reholttumia hudsoniana (formerly treated together with Hoiokula in Pneumatopteris ( Holttum 1977b; Palmer 2003)), Christella , and Menisciopsis by having setulose sporangia and exindusiate sori. Hoiokula is distinguished from Cyclogramma by pinnae incised less than halfway to the costae (vs. more than half-way).Hamate hairs are absent in Hoiokula , but frequent in Cyclogramma and Stegnogramma s.s. Spores of most Stegnogramma and Leptogramma species are echinate, rather than winged, (a feature shared by Hoiokula and some species of Menisciopsis ). Hoiokula further differs from Leptogramma in having costae prominently grooved adaxially, vein endings reaching margins, multiple areoles below the sinuses (except in very small individuals), and presence of zig-zag excurrent veins. Until 2005, both species of Hoiokula recognized herein were treated within Pneumatopteris sandwicensis ; Hoiokula pendens represents one of the most recently recognized native species in the Hawaiian fern flora ( Palmer 2005; Vernon & Ranker 2013; Ranker et al. 2019).

Biogeography and ecology.— Hoiokula is endemic to the Hawaiian Islands, distributed on all major islands ( Palmer 2003, 2005). The two recognized species differ in habit and habitat, with the larger, erect H. sandwicensis occurring in forest understories and along stream margins, and the pendent H. pendens occurring on damp rocks and cliffs, often near streams ( Palmer 2005).

Taxonomic and phylogenetic studies.— Hoiokula bears considerable resemblance to Stegnogramma s.l., and the similarities must have been apparent to Brackenridge (1854), who described the type species in Stegnogramma and illustrated the elongate sori and setose sporangia in the protologue. Both of these features are shared by the three stegnogrammoid genera but are uncommon within Thelypteridaceae . Although Holttum (1977b) treated the plants recognized here in Hoiokula as a species of Pneumatopteris , he noted several characteristics that this “peculiar Hawaiian species” has in common with Stegnogramma , such as “…venation of the apical lamina and a few thick hairs between veins on the upper surface of pinnae, and … somewhat elongate sori” ( Holttum 1982:540).

Based on both concatenated and coalescent analyses (Fawcett et al. in press), the phylogenetic position of Hoiokula is well-supported as sister to the stegnogrammoid ferns, which include the genera Cyclogramma , Stegnogramma , and Leptogramma ( Kuo et al. 2019) . These results should be interpreted with caution, however, since the analysis assumes a bifurcating tree. Preliminary evidence from plastid data (L. Y. Kuo, unpubl. data), and conflicting topologies among gene trees (Fawcett et al. in press) suggest the possibility that this lineage may be of hybrid origin involving Leptogramma and Menisciopsis , which occurs in Hawaii, Melanesia, and eastern Asia. Leptogramma is distributed throughout Asia and India, and is scattered in Africa, Europe, and North America, while the genera Cyclogramma and Stegnogramma s.s. are both restricted to Southeast Asia and Malesia. No species of these three genera have been collected in Hawaii. The hybrid origin hypothesis is currently under investigation (Fawcett, Kuo et al. in prep.).

Figures

FIG.4.A.Hoiokula sandwicensis,Aborn s.n. (VT),pinna lobes,abaxial view.B.Hoiokula pendens,Hobdy2664 (UC),pinna lobes,adaxial view.C.Leptogrammapilosa, Diaz 6621 (UC), abaxial pinna lobes. D. Stegnogramma aspidioides, Palmer 1035 (UC), abaxial pinna. E. Stegnogramma wilfordii, Boufford 20159 (VT), proximal portionof lamina,abaxial view.

FIG. 2. Morphology of the Thelypteridaceae.A. Coryphopteris kolombangarae, SITW07554 (TAIF), glandular indusia.B. Goniopteris yaucoensis, Proctor 43584 (US), stellatehairs along adaxialcosta.C.Pneumatopterisglandulifera,SITW11069 (TAIF),peg-like aerophoresat pinna bases.D.Sphaerostephanospolycarpos,SITW11070 (TAIF),marginally glandular indusia.E.Sphaerostephanos doodioides,SITW05702(TAIF),setoseindusia,spherical glands on indusia,sporangia,and laminar tissue. F. Goniopteris reptans, Wright 813 (US), sori with shriveled, setose indusia, some hairs furcate. G. Macrothelypteris polypodioides, SITW11122 (TAIF), stipe scales. H. Hoiokula pendens, Hobdy 2664 (UC), setulose sporangia. I. Plesioneuron imbricatum, SITW05370 (TAIF), exindusiate sori, sporangia with spherical glands. J. Christella dentata, SITW10525 (TAIF), shriveled,setulose indusia.K. Sphaerostephanos heterocarpos SITW11079 (TAIF),abruptly reduced proximal pinnae,adaxial surface with acicular hairs.L. Coryphopteris subbipinnata, SITW11667 (TAIF),appressed stipe base scales,these marginally setulose.All photos by Cheng-Wei Chen except B,F,and H by Susan Fawcett.