Amblovenatum

Fawcett, Susan & Smith, Alan R., 2021, A Generic Classification of the Thelypteridaceae, Fort Worth, Texas, USA: BRIT Press : 28-29

AMBLOVENATUM

Amblovenatum J.P. Roux, Strelitzia 23:200. 2009, a renaming of Amphineuron Holttum (1971), non Amphineurion ( A. DC.) Pichon— TYPE: Amblovenatum opulentum (Kaulf.) J.P. Roux [= Aspidium opulentum Kaulf. ]— Thelypteris subg. Amphineuron (Holttum) Fraser-Jenk.

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

Etymology.— Gr. amphi, of two kinds + neuron, nerve, pertaining to the venation of the type and some other species in the genus, which varies, even within the same frond, from free, meeting the margin at the sinus, or connivent with a sinus-membrane. Amblovenatum , although not explained by its author, appears to be an inelegantly formed Latin translation of Amphineuron meaning approximately the same thing.

Plants terrestrial, of forested or somewhat disturbed habitats, medium sized (to about 2 m tall); rhizomes long-creeping to erect, with brown setose linear-lanceolate scales; fronds monomorphic, arching to erect, pinnatepinnatifid to pinnate-pinnatisect, stipes dull brown to stramineous; stipe scales tangled, spreading, linear-lanceolate, dark brown and setose, readily deciduous; blades membranaceous to chartaceous, drying bifacially concolorous green to pale-olivaceous, apex subconform to gradually reduced ( A. immersum ); proximal pinnae not reduced, or if reduced, then abruptly; proliferous buds lacking; pinnae short-petiolulate, with truncate bases, proximal pinnae gradually narrowed towards bases, not auriculate (except A. subattenuatum ), margins lobed to within 1 mm of costae, or incised only 1/3 ( A. terminans ) to costae, segments nearly perpendicular to somewhat oblique and falcate, with rounded to broadly acute apices; veins free, connivent at or near sinuses, or with one or more pairs anastomosing below the sinus, and subsequent pairs running to sinus, with both states sometimes present within a single frond ( A. opulentum ), veins ending at margins or terminating prior to margins ( A. terminans ); aerophores present as inconspicuous swellings and/or discoloration at pinna bases; indument abaxially of long (0.5– 1 mm), hyaline, acicular hairs along rachises, costae, and veins, short (<0.1 mm) hairs along rachises, costae, veins, and sometimes laminae, small, clear stipitate glands abundant on laminae between veins, and sulfur-colored spherical, sessile or stipitate glands along costae and veins, most abundant towards segment apices, rarely with scales on costae ( A. distinctum ); indument adaxially of long (0.5– 1 mm) hyaline acicular hairs along rachises, costae, and veins, sometimes with small, colorless stipitate glands on laminae; pustules absent; sori round, discrete to confluent, sometimes sunken in lamina ( A. immersum ), supramedial to inframarginal, often restricted to distal portion of segments, indusiate or exindusiate ( A. distinctum ), indusia thick, brown, sometimes bicolorous, dark in the center and pale towards margins, often bearing abundant sulfur-colored glands ( A. opulentum and A. immersum ) and/or setae ( A. terminans ); sporangia with thin stalks, which may bear stipitate glands, capsules glabrous; spores dark brown to black, rarely tan ( A. subattenuatum ), perine with low thin crests; x =36, two species counted: A. opulentum is tetraploid, but both diploid and tetraploid counts are reported for A. terminans . One collection from Timor may represent an infrageneric hybrid between A. opulentum and A. immersum , and A. tildeniae , of the Society and Cook islands, may represent an intergeneric hybrid between A. opulentum and Christella dentata ( Holttum 1977b) . Putative hybrids from the Cook Islands, between A. opulentum and Christella dentata (Game 92/128,! UC), and A. opulentum and Strophocaulon invisum (Game 89/172 A, 89/173,! UC) have been reported by Game and Smith (2014).

Diagnosis.— Amblovenatum s.s. is distinguished from Mesopteris s.l. by the presence of long (0.5– 1 mm) hyaline acicular hairs on axes of abaxial or adaxial laminae (vs. only minute stipitate glands or hairs> 0.5 mm long); sori typically with large, persistent conspicuous indusia (vs. sori exindusiate, with small indusia, or indusia obscured by copious resinous glands); membranaceous to thin-chartaceous laminae drying bifacially concolorous green to olivaceous (vs. thick-chartaceous laminae sometimes drying bicolorous dark brown to reddish); by the presence of opaque whitish to sulfur-colored glands (vs. translucent red or amber resinous glands)—though both genera frequently have minute colorless or golden brown stipitate glands as well; sori often restricted to distal veins of segments (vs. sori distributed the length of segments, or restricted to proximal portion of segments); and sinus membranes rarely bearing an appendage (vs. sinus-membrane usually with conspicuous projecting appendage). Christella differs in having more abundant hairs, especially on laminar tissue between veins, and often having characteristic orangish pear-shaped glands.

Biogeography and ecology.— Amblovenatum is recognized herein as a genus of only six species. One of these, A. opulentum , is widespread throughout the tropics. Its native range is ostensibly Australasia south to Queensland, Asia north to Hainan, west to Sri Lanka, throughout Malesia, and east to Tahiti. The earliest records we have found outside this range are from 1948 in Mozambique (Mendonza 4377, L), and 1938 in Martinique ( Smith 1971:110, Stehle & Stehle 4986, UC, US; GBIF.org). This species is now widespread throughout the Antilles, Central America, much of South America, and East Africa and Madagascar; it may be extirpated in Florida ( Nelson 2000), where it was once established in Dade Co. Holttum (1982) noted that it was not common anywhere in Malesia, and of doubtful nativity in Java, but that cultivated plants in Singapore had a tendency to naturalize in the vicinity. Like Christella dentata and Macrothelypteris torresiana , it may be a successful weed where it has become established. Amblovenatum terminans occupies a native range similar to that of A. opulentum , but it extends east only as far Queensland and New Guinea; it is represented in Africa by few collections ( Holttum 1974a) and may be introduced there. The species A. queenslandicum was described relatively recently ( Holttum 1986) and is endemic to Queensland, Australia.

Taxonomic and phylogenetic studies.—Amphineuron was described by Holttum (1971) and its ten species were monographed by him a few years later ( Holttum 1977a). His circumscription was adopted by Ching (1978), with the exception of the east Asian endemic species that Ching segregated in a newly described monotypic genus, Mesopteris , as M.tonkinensis . Because of some uncertainty regarding relationships among genera,the remaining species of Amphineuron were treated in a broad concept of Cyclosorus in the Flora of China, though Mesopteris was maintained based on morphological and molecular evidence ( Lin et al. 2013).Because of its similarity to the older name Amphineurion (Apocynaceae), also native to southeast Asia, the name Amphineuron was rejected (Middleton in Brummitt 2007), and Amblovenatum was published as its replacement ( Roux 2009).

In his revision of Amphineuron, Holttum (1977a: 206) recognized that the species “may be divided into two groups, one with conspicuous indusia, the other with indusia small or lacking.” These two groups correspond to Amblovenatum s.s. and Mesopteris s.l. in our treatment. Despite some morphological similarities, these two groups are not closely related, based on molecular phylogenetic evidence, which was first demonstrated by He and Zhang (2012) and corroborated by subsequent analyses (Fawcett et al. in press). Amblovenatum s.s. is well supported as a member of the christelloid clade, but because of poor resolution of backbone nodes, its closest relatives within the clade are uncertain. The Mesopteris clade, which includes the Chinese/Vietnamese endemic, M. tonkinensis , and several Malesian and Australasian species, is in the chingioid clade, sister to a clade that includes Grypothrix , Menisciopsis , Chingia , and Plesioneuron ( Fig. 1 ).

Figures

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