Sphaerostephanos, J. Sm., J. Sm.

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 79-81

SPHAEROSTEPHANOS

Sphaerostephanos J. Sm. in Hooker, Gen. Fil., t. 24. 1839.

— Thelypteris subg. Sphaerostephanos (J. Sm.) K. Iwats., Mem.Coll.Sci Univ. Kyoto, ser. B, 31:32.1964.— TYPE: Sphaerostephanos asplenioides J. Sm. [= S. polycarpos (Blume) Copel.]

Haplodictyum C. Presl

Mesochlaena ( R.Br.) J. Sm.

Proferea C. Presl

For additional generic synonymy, see Holttum (1974a, 1977b, 1982).

Etymology.—Gr. sphaera, sphere + stephanos, crown, in reference to the spherical yellow glands adorning the sori; these may be borne on the receptacles, indusia ( Fig. 2D ), or sporangia, and are characteristic of the genus.

Plants mostly terrestrial, or occasionally cremnophilous or rheophytic, mostly from (10–)30–100(–200) cm tall; rhizomes mostly suberect or erect, occasionally short-creeping, rarely long-creeping or scandent ( S. scandens Holttum ); fronds monomorphic or with fertile fronds smaller and more erect (fronds subdimorphic to dimorphic, e.g., S. dimorphus ), usually pinnate-pinnatifid or once-pinnate, rarely pinnae subentire, pinnatifid or weakly divided, with elongate apical lamina subtended by reduced lateral pinnae as in S. beccarianus ( Fig. 7B ) and related species (no simple-bladed or twice-pinnate species known), usually arching; stipes stramineous or brownish, usually dull, stipe bases and rhizome scales brown to tan, ovate to lanceolate, rarely glabrous, thin, usually with acicular, hyaline hairs 0.1–0.2 mm on margins and surfaces; blades usually chartaceous, less often thicker and subcoriaceous to coriaceous (species of more open areas, e.g., S. lithophyllus ), usually drying green, lanceolate, ovate to deltate, proximal pinnae usually subabruptly or abruptly reduced ( Fig. 2K ), occasionally gradually reduced, often> 6 pairs (to 30+ pairs, e.g., in S. sagittifolius ), basal pair(s) often auriculiform or glanduliform and <5 mm long, blade apex gradually reduced, with distal pinnae not or only slightly decurrent, or subabruptly reduced and pinna-like; proliferous buds absent in axils of distal pinnae (no gemmiferous spp. known); pinnae entire (e.g., S. debilis , S. dimorphus , S. mutabilis ) to subentire, crenate, shallowly lobed, or often pinnatifid to more than half their width, rarely pinnatisect or lobed within 1 mm of costae (e.g., S. novoguineensis , S. williamsii ), typically straight, sometimes with small acroscopic auricles at pinna bases, adaxially grooved; veins usually prominent abaxially and adaxially (readily seen without transmitted light), lowermost pair from adjacent segments running to margin at a sinus between adjacent lobes, usually united to form an excurrent vein that runs to sinuses, or with 2–4 pairs (exceptionally 10 pairs united in S. maximus ) united and forming a common excurrent vein (straight or zig-zag) that runs to a sinus, rarely lowermost veins meeting margins above sinuses (e.g., S. novoguineensis , S. williamsii ), free veins ending at pinna margins; aerophores absent or often present at pinna bases, if present then swollen, tuberculate, or rod-like to 2 mm long (these species generally producing mucilage during development), or, forming a small patch of darkened aerating tissue at pinna bases; indument abaxially usually of hyaline acicular hairs on rachises, costae, veins, and sometimes between veins, rarely the blades glabrous or nearly so (e.g., S. cataractorum , a rheophyte from the Admiralty Islands), indument adaxially of hyaline or sometimes reddish acicular hairs on rachises and costae, sometimes also on veins and between veins, hairs often appressed between veins, scattered to dense, hairs on stipes and rachises short to long, 0.1–1(–2) mm, sparse to dense, rarely blades glabrous or glabrescent, usually single-celled, rarely septate; glands, if present, resinous or hemispherical and opaque, usually light yellowish to light orangish, seldom capitate (short-stipitate), borne on laminae and veins abaxially and sometimes also adaxially; pustules generally absent on laminar tissue (present in some spp., e.g., S. beccarianus , Fig. 7A ); sori inframedial, medial, or infrequently submarginal, usually round, less often oblong or elongate along veins in a few spp. (e.g., the type), indusiate or exindusiate, indusia if present usually round-reniform or reduced to a fragment, usually whitish or tan when young, persistent to evanescent, hairy and/or glandular to glabrous ( Fig. 2D, 2E ); sporangia often setulose or with sessile glands just below the annulus like those of lamina; spores pale brown, lacking pronounced winglike ridges or echinae, reticulate and perforate (fenestrate), secondary sculpturing gemmulate ( Tryon & Lugardon 1991); x = 36, ten species counted, mostly diploid, tetraploid counts few in comparison.

Diagnosis.—The most morphologically similar genera to Sphaerostephanos are other cyclosoroid genera, including the closest relatives, Pneumatopteris s.s., Reholttumia , Pronephrium s.s., and several other more distantly related christelloid genera— Christella s.s., Pseudocyclosorus , Amblovenatum , and Abacopteris . Most of these, except for Pseudocyclosorus and some Amblovenatum , have at least a single pair of veins (if not many more) anastomosing below the sinuses and with an excurrent vein to the sinus. All have a base chromosome number of x = 36. All occupy large areas in continental Asia and Malesia, with extensions into India, Melanesia, Polynesia, and Australasia for some species. In the Flora of China ( Lin et al. 2013), most of the christelloid genera mentioned above, including Sphaerostephanos , were treated as part of a greatly expanded concept of Cyclosorus , except for a separately treated Pseudocyclosorus and Pronephrium s.l. (which included Abacopteris ). However, the Flora of China contains only four species of Sphaerostephanos , an extremely depauperate representation of the genus. Co-occurrence of many genera, recent and rapid diversification, and a lack of taxonomic experts in the group have made classification and identification of cyclosoroid Thelypteridaceae especially difficult and somewhat contentious. Rampant homoplasy in Sphaerostephanos and related genera has caused great difficulty in delineating taxa. As may be expected for a genus with more than two hundred species occupying diverse habitats, there is no single morphological character known that reliably holds the genus together—rather one must utilize a suite of characters, and have complete fertile specimens (including rhizomes) for identification to genus. Nevertheless, the circumscription of the genus by Holttum (1982) corresponds very closely to a clade, with only minor adjustments. The following characteristics are common to most (but by no means all) species: short-creeping to suberect or erect rhizomes, with lanceolate, brownish, hairy scales at apices (as well as at stipe bases); pinnate fronds with entire, subentire, crenate, or shallowly to deeply lobed pinnae, i.e., blades once pinnate to pinnate-pinnatifid; veins anastomosing, with at least the lowermost pair from adjacent segments uniting at an obtuse angle and producing an excurrent vein that runs to the sinus or to the excurrent vein in the next areole (thus bisecting the areole), i.e., veins sometimes meniscioid with as many as four pairs (10 pairs in S. maximus ) joined in a file between costa and pinna margin; abruptly or subabruptly reduced proximal pinnae; costae abaxially with spreading to curved-appressed hairs, these often stout; the presence abaxially, and less often adaxially, of sessile, spherical or somewhat flattened, yellowish to light orangish, transparent glands on the laminar tissue between veins, on veins, and on costae and costules; often appressed or ascending (distally pointed) acicular, hyaline hairs between the veins adaxially, these often thin, mostly 0.1–0.3 mm long; the absence of pustules on laminar tissue; and x = 36.

Biogeography and ecology.—Species occur mostly at low and middle elevations, from near sea level to ca. 1500 m, with a few to 2000 m, and even fewer to 3000 m (to 3750 m, in subalpine shrublands and grasslands, e.g., S. archboldii , from New Guinea). Many of the 190 species of Sphaerostephanos are highly localized, endemic to relatively small areas, and found mostly in primary, undisturbed forests. However, as with many thelypteroid genera, some widespread spp. (e.g., S. heterocarpos, Fig. 2K ) occur in disturbed forests, at forest margins, and sometimes in open areas; occasionally they grow on rocks or streamsides, where they tend to form smaller , less conspicuous adult plants. A few are rheophytes, e.g., S. debilis , S. mutabilis , with very narrow, streamlined, sometimes nearly glabrous pinnae. Some species are weedy and found especially along roadsides, trails, and wet ditches. The major center of diversity for Sphaerostephanos in the Paleotropics is unquestionably Malesia, with 150+ spp.; Melanesia and Polynesia are lesser centers of diversity. New Guinea is especially species-rich, with 60+ spp., most of them narrowly endemic and many of them poorly known.

Shortly after he expanded the concept of Sphaerostephanos from six species to more than 120, Holttum (1971, 1975, 1982) enlarged his concept still further, and described many new species, recognizing 152 spp. from Malesia, 12 species from tropical mainland Asia, 17 spp. from Polynesia and Australasia ( Holttum 1977b), and four spp. from Africa and islands in the Indian Ocean ( Holttum 1974a); most of the species he assigned to Sphaerostephanos , especially those from Malesia, Melanesia, and Polynesia, remain in that genus in our reclassification. However, we still include only two of the four species Holttum (1974a) recognized from Africa and islands of the Indian Ocean, S. arbuscula and S. subtruncatus , in Sphaerostephanos . About ten spp. are known from continental Asia including both of the African and Indian Ocean species, which also occur in India and Sri Lanka. The others are S.gaudichaudii , S. heterocarpos, S. latebrosus , S.penniger , S. polycarpos, S. productus , and S. validus , five of which also occur in western Malesia (see Holttum 1979). Species we exclude from Sphaerostephanos , where they were placed by Holttum, are noted below. No species are known from the New World.

With the addition of 15 species newly combined below, and placement of several species in other genera (see also below), there are about 190 known species in Sphaerostephanos , making it the second largest genus in the family, behind only Amauropelta . In Holttum’s 1982 treatment, 66 taxa in Sphaerostephanos were known only from the type or one or two other collections, a testament to both their rarity and the paucity of herbarium collections. We are confident that there are dozens of undescribed species belonging to Sphaerostephanos , especially in eastern Malesia, where there are likely undiscovered narrowly distributed endemics; in addition, some more wide-ranging species, e.g., S. heterocarpos, are likely species complexes, in need of refinement and further study. Clearly, the genus is under-collected, because of the many superficially similar and highly local species and lack of specialists in the group.

Taxonomic and phylogenetic studies.—Until Holttum (1971) presented a new system of genera for Thelypteridaceae , Sphaerostephanos was a name applied to Old World species with elongate, indusiate sori, e.g., the type, Sphaerostephanos asplenioides J. Sm. [= S. polycarpos (Blume) Copel.]; this group comprised about six species. Holttum expanded his concept of Sphaerostephanos to include many species with round sori, and also some exindusiate species. Other salient characteristics of Sphaerostephanos included species with many pairs of gradually to often abruptly or subabruptly reduced proximal pinnae; veins mostly united below sinuses and forming a series of one to about four areoles, each with an included, excurrent veinlet, or with the excurrent veinlet continuous from one areole to the next; sessile, hemispherical, opaque, yellowish to light orangish glands usually present on the costules, veins, and often between the veins abaxially and sometimes also adaxially; sporangia slender-stalked and with sessile glands or setulae near the annulus; light brown spinulose spores; and x = 36. Although Holttum included species in Sphaerostephanos that were exceptional (deviated from the “norm”)in some of these characteristics,most species could be comfortably placed in Sphaerostephanos on the basis of possessing a combination of these salient features.

Sphaerostephanos exhibits extremely wide variation in frond type, blade size, blade dissection, number and degree of reduction of proximal pinnae, and blade apex (conform or gradually reduced), with long aerophores or none at all, remarkably varied indument (glands and hairs), and presence or absence of indusia. There are diminutive species with few, small, entire pinnae, like S. obtusifolius , and S. ddebilis (pinnae ca. 10 × 2 mm), both from New Guinea, to large species with fronds> 1.5 m, pinnae to 30 × 2.5 cm (e.g., S. braithwaitei , from the Solomon Islands), species with 30+ pairs of small greatly reduced proximal pinnae (e.g., S. sagittifolius ) and species with deltate blades—the lowest pinnae the longest and with reduced pinnae entirely absent. A group of related, pinnatifid or weakly divided species with just a few pinna pairs is exemplified by S. beccarianus ( Fig. 7B ), formerly included by Holttum (1972, 1982) in Pronephrium sect. Pronephrium . There are rheophytes with relatively few, entire pinnae 20+ times longer than wide and very narrow (<5 mm), with only a single row of sori along each side of the costae (e.g., S. mutabilis ). In short, just about any blade type imaginable can be found in the genus, short of forking gleicheniaceous blades or indeterminant ones. Some species have very long-creeping, narrow rhizomes, and bilaterally produced fronds, like S. pentaphyllus , thus mimicking some species of Grypothrix but lacking their hamate hairs; others form erect , relatively long trunks, e.g., S. braithwaitei and S. archboldii , to 60 cm tall in the latter.

In broadly based molecular analyses, Sphaerostephanos is monophyletic with minimal departure from previous classifications. Within the genus, there are two major clades, and a small clade of early diverging species (e.g., S. larutensis and S. oosorus ; both are taxa with elongate sori). One of the two major clades includes many of the pinnate-pinnatifid taxa that tend to be hairy on both laminar surfaces (e.g., S. heterocarpos, Fig. 2K ), while the second major clade includes several once-pinnate species to shallowly lobed species (e.g., S. confertus ), including the taxa previously treated by Holttum (1982) in Pronephrium sect. Pronephrium . Sphaerostephanos is sister to newly redefined Pneumatopteris s.s. (Fawcett et al. in press; Fig. 1 ). This clade is in turn sister to Reholttumia and then Pronephrium s.s. (corresponding largely to Holttum’s sect. Dimorphopteris). Together these four genera comprise the sphaerostephanoid clade. More distant relatives include members of the pseudocyclosoroid clade ( Abacopteris , Amblovenatum , Christella s.s., and Pseudocyclosorus ), and Strophocaulon (whose two members include two very widespread spp. formerly placed in Sphaerostephanos by Holttum, 1982). All of these genera pertain to the christelloid clade, and most (except Pseudocyclosorus ) contain species that usually have at least one pair of anastomosing veins, meeting at an obtuse angle below the sinuses and with an excurrent vein. Many, but not all, of these genera have reduced (sometimes greatly reduced) proximal pinnae, and most have sori with round-reniform indusia (but this lost in several evolutionary lines).

Most necessary combinations have been made in Sphaerostephanos by Holttum (1979, 1982), who included also homotypic and heterotypic synonyms in his revisions. We make combinations for the following species, placed by Holttum in other genera, especially Pronephrium .

Figures

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.

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).