Heterospathe elegans (Becc.) Becc., Nova Guinea 8: 205 (1907)

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Distribution

Map uses TDWG level 3 distributions (http://www.nhm.ac.uk/hosted_sites/tdwg/geogrphy.html)
New Guineapresent (World Checklist of Arecaceae)A

Discussion

  • A relatively broad concept of Heterospathe elegans that incorporates both H. humilis and H. versteegiana has been employed here, as a pragmatic solution to a taxonomically problematic group. Widespread in montane and submontane regions with an elevation of 500 - 2200 m, H. elegans is a small understorey palm recognisable by its elongate inflorescences, where the first peduncular bract is inserted above the tip of the prophyll, in the distal quarter of the peduncle. A highly variable species, it may be acaulescent or have a slender stem up to 2.5 m. Leaf division appears to be highly plastic and varies from entire to pinnately divided into 6 - 43 leaflets. Leaves are predominantly divided into 20 - 40 single-fold leaflets, with multiple folds in the apical and basal leaflet pair, although other combinations of leaflet folding also occur (Fig. 1). We are confident that the broad species concept we have employed is a useful and realistic way of circumscribing Heterospathe elegans. The specimen Moore & Millar 9262, an unusually generous collection with extensive notes, photographs, numerous leaf portions and 16 separate inflorescences, clearly illustrates the variation which can be found in a single locality. This specimen proves that the habit may be either solitary or clustering and the leaves are divided into a wide range of single and multi-fold combinations. The inflorescences are branched to either one or two orders and sometimes have a second, inconspicuous peduncular bract. The peduncle ranges from a very slender diameter of 1.5 mm to a moderately robust 4.5 mm (both measurements taken on the widest line of the peduncle, which is ellipsoid in cross-section), and the entire length of the inflorescences ranges from approx. 70 - 130 cm. Due to the high levels of variation that can be present in a single locality, less copious specimens of H. elegans may represent only a small proportion of the variation present in a population. While we initially considered recognising a number of more narrowly defined species, specimens such as Moore & Millar 9262 demonstrate that a broad species concept is more appropriate. Despite the broad species concept we employ for Heterospathe elegans, two distinct morphotypes merit formal recognition at infraspecific level, one taxon being acaulescent, the other bearing an aerial stem. From our own field experience and from herbarium specimen label data, we find no evidence that both morphotypes occur sympatrically in single populations. The geographical distribution of the two taxa is quite highly structured, with the majority of records for the stemmed taxa concentrated in the southwestern part of the species distribution to the exclusion of the acaulescent taxon, which predominates elsewhere (Map 1). In view of this geographical differentiation, we have decided to recognise the two taxa at subspecies level. We have not recognised two distinct species because no further robust correlated characters could be identified. Thus, H. elegans subsp. elegans is identified by the presence of a stem up to 2.5 m, whereas H. elegans subsp. humilis is acaulescent with a short horizontal stem which roots along its length (Fig. 1). Additional local morphological variants may be recognisable within the broader variation of Heterospathe elegans. Specimens from Mt Turu in East Sepik Province, Papua New Guinea, have leaflets in pairs, a feature that is not known to occur in other areas. Specimens from Finschhafen in Morobe Province, Papua New Guinea, have unusually large, spreading inflorescences. Recognisable local forms are likely to be present in other areas, and this may be worthy of further investigation when more specimens are available. However, the information available at present is insufficient to justify formal recognition of further regional variants. Two specimens of the Heterospathe elegans complex were included in the molecular study of Heterospathe carried out by Norup et al. (2006), Banka et al. 2011 (H. elegans subsp. humilis) and Baker et al. 1130 (H. elegans subsp. elegans). Of the two low copy nuclear genes studied, only one (PRK) could be sequenced for Baker et al. 1130. The strict consensus tree resulting from parsimony analysis of PRK places the two accessions on different branches within the Heterospathe clade (Norup et al. 2006), which undermines our taxonomic decision here. However, the resolution and bootstrap support for relationships among Heterospathe species in this tree are poor and without more thorough DNA analyses, the available data do not overturn the taxonomy presented here, which is so strongly supported by morphological evidence. Berlin was identified by Beccari as the herbarium housing specimen material for Heterospathe elegans (Beccari 1905). Unfortunately this holotype material was destroyed, and the only other type material we have been able to identify is a sheet of H. elegans at FI, which has been annotated by H. E. Moore Jr. as an isotype. This specimen was collected by Schlechter, but is sine numero whereas the protologue cites the collection number 14071. Locality and date information match those of the type in the protologue, and the specimen itself is a good match for Beccari?s detailed description. Additionally, this is the only sheet identified as H. elegans (as B. elegans) material in the Herbarium Palmarum at FI (Cuccuini & Nepi 2006), where the majority of Beccari?s types are held. For these reasons we concur with H. E. Moore Jr. and regard this as isotype material. Beccari described Heterospathe elegans as a slender, graceful palm, with an ordinary stem that apparently resembles that of an Iguanura or a walking stick (Beccari 1905). He noted that he had not seen stem material and that his description of the stem and habit was assumed from the leaf, inflorescences and fruit which formed the type specimen. Given our current knowledge of the morphology and distribution of the H. elegans complex, we agree with Beccari that it is likely the type specimen of H. elegans came from a palm with a stem and we designate an epitype to allow precise application of the name. The type specimens for H. versteegiana and H. humilis also lack stem material or notes describing the habit. However, Beccari?s protologues for these species very clearly describe the habit (and the stem in the case of H. versteegiana) which leads us to believe that he had access to other supporting information when he was writing the descriptions. Therefore we have allowed Beccari?s descriptions to guide us in choosing epitypes for these names. In all cases we have attempted to minimise the distance between collection localities of the original type and the newly designated epitype, and to ensure that other morphological characters match as closely as possible. (Trudgen, M.S. and Baker, W.J. 2008. A revision of the Heterospathe elegans (Arecaceae) complex in New Guinea. Kew Bulletin, Vol. 63, pp 639-647)B

Description

  • Slender, solitary or clustering, understorey palm, acaulescent or with aerial stem to 2.5 m, bearing 7 - 12 (-18) leaves per crown. Stem 1 - 5 cm in diam., with persistent leaf bases towards the apex; internodes 1.5 - 3.5 cm. Leaf 1 - 3.3 m long including petiole; sheath indistinct or to 42 cm, margins fibrous; petiole 42 - 130 cm long, concave adaxially, rounded abaxially; rachis 20 - 140 cm long; pinnately divided (occasionally entire) with 6 - 43 leaflets each side of rachis; leaflets arranged regularly or rarely in pairs, borne 1 - 10 cm apart, adaxial surface dark green, abaxial surface green, ramenta (if present) to 2.4 mm long, attached to abaxial midvein for up to ¾ the leaflet length, small brown scales sometimes present on abaxial leaflet surface; middle leaflet 21 - 58 cm long, 1 - 2.75 cm wide, sigmoid, with 1 - 8 folds, transverse veinlets inconspicuous; apical leaflets 9.5 - 43 cm long, 0.4 - 4.5 cm wide, sigmoid to linear, 1 - 10 folds. Inflorescence 65 - 150 cm long, interfoliar, elongate, branched to 1 - 2 orders; prophyll 12.5 - 46 cm long, 0.5 - 2 cm wide, flattened, splitting apically; peduncular bracts 1(-2); first peduncular bract 12.5 - 60 cm long, 0.25 - 1.5 cm wide, tubular, inserted above the tip of the prophyll in the distal quarter of the peduncle; splitting lengthwise or rarely detaching basally to leave a 1 - 2 cm collar-like remnant; second peduncular bract (if present) 0.1 - 1.5 cm long; peduncle 50 - 140 cm long, 1.5 - 5.5 mm wide, ellipsoid in section, often covered with tomentum which is more dense above the insertion of the first peduncular bract; first order branches 4 - 16, to 26 cm long, 0.5 - 5.5 cm apart, with up to 7 rachillae; rachillae 5 - 17 cm long, 1 - 2 mm diam.; triads up to 2 mm apart, arranged spirally, lacking female flowers in distal quarter of rachilla. Male flower 1.8 - 3.8 mm long, 1.5 - 2.6 mm diam. at anthesis; sepals 3, 1 - 2 mm long, 1.5 - 2.5 mm wide, imbricate, green, margins sometimes ciliate; petals 1.4 - 3mmlong, 1.2 - 3 mm wide, valvate, triangular, green, striate when dry; stamens 6; filaments 0.8 - 1.9 mm long, free, inflexed; anthers 1 - 2 mm long, 0.2 - 1.5 mm wide, curved, yellow, dorsifixed and versatile, latrorse, connective dark brown; pistillode 0.8 - 1.8 mm long, 0.2 - 0.5 mm in diam. at middle, straight or slightly tapered, trifid, dark red-brown. Female flower 1.5 - 2.9 mm long, 1.7 - 2.9 mm diam.; sepals 3, 1.5 - 2.4 mm long, 1.3 - 2.5 mm wide, imbricate, cucullate, margins often ciliate; petals 3, 1 - 2.3 mm long, 0.7 - 1.7 mm wide, imbricate with valvate apices; gynoecium 1 - 2 mm long, 0.8 - 1.8 mm in diam., globose, stigma minute. Fruit 10 - 15 mm long, 8 - 10 mm in diam., globose with small, subapical stigmatic remains, bright red or orange; endocarp 8 - 10 mm long, c. 6 mm in diam., pale brown, very thin, often adheres to seed. Seed 5 - 8 mm long, 5 - 8 mm in diam., globose; endosperm ruminate; embryo basal. (Trudgen, M.S. and Baker, W.J. 2008. A revision of the Heterospathe elegans (Arecaceae) complex in New Guinea. Kew Bulletin, Vol. 63, pp 639-647)B