Pelazoneuron

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 62-63

PELAZONEURON

Pelazoneuron (Holttum) A.R. Sm. & S.E. Fawc. , gen. et stat. nov. — Christella sect. Pelazoneuron Holttum, J. S. African Bot. 40:144. 1974.

— Type: Pelazoneuron patens (Sw.) A.R.Sm.& S.E. Fawc. [= Polypodium patens Sw. ]

For more complete synonymy, see Smith (1971).

Etymology.—Gr. pelazo, to approach + neuron, vein, in reference to the connivent veins at or just below the sinus, which are near each other, rather than anastomosing at an obtuse angle, as in Christella s.s. and many other related genera.

Plants terrestrial, or occasionally in rocky crevices, medium-sized to very large (fronds 40–250 cm long); rhizomes short- to long-creeping, or, in a few species, suberect to erect and forming small upright trunks (e.g., P. patens ); fronds monomorphic, pinnate-pinnatifid, erect or arching; stipes stramineous to tan, darkened at the very base, adaxially grooved, bearing scales at the base like those of rhizome apices; stipe scales lanceolate to occasionally ovate-lanceolate, brown, setose on margins and surfaces, occasionally the scales ovate-lanceolate and glabrous (e.g., the type, P.patens ); blades chartaceous to subcoriaceous, drying greenish, pinnae generally pinnatifid or pinnatisect, proximal ones the longest or nearly so, very rarely greatly reduced, distal ones gradually or sometimes abruptly reduced, blade apex not conform or rarely subconform ( P. serra ); rachises always lacking proliferous buds; pinnae opposite or nearly so proximally, becoming alternate distally, adaxially with a groove that is not continuous with the rachis groove, shallowly to often deeply pinnatifid; veins usually prominent on both sides, one or sometimes two pairs from adjacent segments connivent at an acute angle at or very slightly below the sinus ( Fig. 7D ), or the distal one or a pair meeting segment margin just above the sinus (veins not forming areoles) ( Fig. 7C ), rarely with a single pair truly obtusely united below the sinus and with an excurrent vein running to sinus, vein endings reaching segment margins; aerophores absent at pinna bases, or pinnae with a slightly raised and darkened lunate ridge at attachment to rachis; indument abaxially of stipes, rachises, costae, veins, and sometimes laminar tissue between veins of hyaline acicular, unicellular hairs, blades sometimes glabrescent with age, or blades sometimes lacking hairs on the lesser veins and between veins, most species lacking costal scales, but these scattered or more numerous in a few species (e.g., P.serra , P.augescens , P. tuerckheimii ); indument adaxially of generally long (> 0.5 mm) hyaline, unicellular acicular hairs on stipes, rachises, and costae, sometimes also on veins, and in a few species (e.g., P. kunthii ) with scattered hairs between veins; pustules absent on laminar tissue on both sides; sori medial or nearly so, not usually coalescent at maturity, indusiate, indusia glabrous to usually setose and somewhat persistent; sporangia without setulae or glands on the capsules, or each with a small clavate unicellular colorless glandular cell on the stalk; spores dark brown, with perispore variously ridged, rugose, or echinulate; x = 36 (10 of 16 spp. counted), diploids and tetraploids known, and several interspecific hybrids ( Smith 1971).

Diagnosis.— Pelazoneuron differs from Christella in having the lowermost veins from adjacent segments connivent at an acute angle at the sinuses (vs. united at an obtuse angle below the sinus and with an excurrent vein to the sinus) and in having the proximal pinnae the longest or nearly so. Pelazoneuron differs from Pseudocyclosorus , which has similar venation, in the deltate blades with proximal pinnae the longest, or nearly so (vs. many pairs of abruptly reduced proximal pinnae). Pelazoneuron differs from many other cyclosoroid genera in one or often more of the following characteristics: lack of protruding aerophores at pinna bases; relatively large, ± persistent indusia; lack of areolate venation and included veinlets; monomorphic fronds; lack of laminar buds; lack of sessile, resinous glands on veins and laminar tissue; generally long-creeping rhizomes; and somewhat weedy nature in semi-open habitats.

Biogeography and ecology.—The 16 known species and four varieties are restricted to the New World tropics and subtropics, from the southern U.S.A. through the Antilles, Mexico, Central America, and South America to northern Argentina , Paraguay, Uruguay, and Bolivia ( Smith 1971); one species ( P.kunthii ) is known to be naturalized in Spain and perhaps East Africa. Most species are at least locally common, if not weedy, and occur at low to middle elevations, to ca. 2600 m in the tropics, and are found along roadsides, trails, ditches, ravines, and limestone outcrops, often in slightly disturbed, somewhat open places.

Taxonomic and phylogenetic studies.—Holttum described Christella sect. Pelazoneuron in his treatment of the Thelypteridaceae of Africa (1974a) and considered most African species of Christella to belong to this section, in addition to many of the neotropical species; he selected one of these, Christella patens , as the type. Molecular data have shown Pelazoneuron to be rather distantly related to Christella ( Smith & Cranfill 2002; Almeida et al. 2016; Patel et al. 2019a; Fawcett et al. in press). Other neotropical genera of the family ( Amauropelta , Cyclosorus , Goniopteris , Meniscium , Stegnogramma , and Steiropteris ) are also distantly related to Pelazoneuron , which is sister to a large clade that includes predominantly paleotropical genera. Although molecular data are not available for many African species of Christella , we find evidence that African members of Christella sect. Pelazoneuron sensu Holttum (e.g., C. chaseana and C. gueinziana ) are more closely allied to Christella s.s. and Pseudocyclosorus than to the type of Pelazoneuron (Fawcett et al. in press). Our circumscription of the genus is largely as treated in Smith (1971) as Thelypteris sect. Cyclosorus , with the exclusion of a few species that are now placed in other genera. Among the neotropical taxa in that treatment, three are now included in Christella ( C. conspersa , C. dentata , C. hispidula ), one in Cyclosorus s.s. ( C. interruptus ), and another, the widely naturalized species Thelypteris opulenta , is now placed in the paleotropical genus Amblovenatum . All of the American species now placed in Christella , Cyclosorus , and Amblovenatum have the lowermost veins from adjacent segments truly united at an obtuse angle below the sinuses, producing an excurrent vein from this union that runs to the sinus, a condition largely absent in Pelazoneuron .

Notes.—Based on phylogenetic analyses (Fawcett et al. in press), two varieties, Pelazoneuron ovatum var. lindheimeri and Thelypteris patens var. dissimilis , are not sister to the typical varieties of their species. We refrain from making a combination for the latter, pending further study, but do provide one for P. ovatum var. lindheimeri . Additionally, Smith (1971) hypothesized that P. kunthii may be of hybrid origin, involving Christella hispidula and Pelazoneuron ovatum , based on its intermediate morphology (e.g., hairs on adaxial laminae between veins, and some veins anastomosing). Although this taxon is recovered with high support as a member of the Pelazoneuron clade in both concatenated and coalescent analyses (Fawcett et al. in press), we do find support for the hypothesis proposed by Smith (1971) based on the discordant topologies of individual gene trees.Two other taxa in the Pelazoneuron clade, Thelypteris patens var. dissimilis and P. schizotis , exhibit similar patterns of discordance, and all three taxa are currently the subject of further investigation.

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.