A contribution to the systematics of Xylopia (Annonaceae) in Southeast Asia
TL;DR: 23 Xylopia species in the Sundaic region of Southeast Asia are recognised, and evidence that additional collecting and taxonomic analysis in the region is needed is provided.
Abstract: Herbarium and field study of Xylopia L. (Annonaceae) for the Flora of Peninsular Malaysia and the Flora of Thailand projects has clarified regional diversity patterns within this ecologically significant lowland rainforest genus. Two species groups represented within Southeast Asian floras are delineated, one centred on Xylopia ferruginea (Hook.f. & Thomson) Baill. and the other on Xylopia malayana Hook.f. & Thomson. In the Xylopia ferruginea group, a new species, Xylopia erythrodactyla D.M.Johnson & N.A.Murray, is distinguished from X. ferruginea, and a new combination, Xylopia sumatrana (Miq.) D.M.Johnson & N.A.Murray, is proposed, based on an earlier name for the species currently known as Xylopia stenopetala Oliv. In the Xylopia malayana group, review of the species Xylopia elliptica Maingay ex Hook.f. & Thomson resulted in the recognition of three additional species: Xylopia platycarpa D.M.Johnson & N.A.Murray, from southern Thailand and northwestern Peninsular Malaysia, Xylopia ngii D.M.Johnson & N.A.Murray, from Peninsular Malaysia, Sumatra and Borneo, and Xylopia heterotricha D.M.Johnson & N.A.Murray, from Sumatra and Borneo. The taxon Xylopia malayana Hook.f. & Thomson var. obscura Kochummen is placed in synonymy under Xylopia elliptica sensu stricto. Xylopia fusca Maingay ex Hook.f. & Thomson var. sessiliflora Kochummen & Whitmore is distinguished from Xylopia fusca, and raised to species status as Xylopia sessiliflora (Kochummen & Whitmore) D.M.Johnson & N.A.Murray. We recognise 23 Xylopia species in the Sundaic region of Southeast Asia, and provide evidence that additional collecting and taxonomic analysis in the region is needed.
Summary (2 min read)
- The Annonaceae, a flowering plant family of 2500 species, including the economically important soursop, custard apple and ylang-ylang, is widespread across the tropics.
- Corlett & Turner (1997) determined that Annonaceae ranked fourth in species-richness among flowering plant families in Singapore; Appanah et al. (1993) found that Annonaceae ranked first in species diversity among lianas of Malaysian forests.
- A full treatment, including keys and distribution maps, is forthcoming.
- Conservation assessments using IUCN (2012) criteria are not included in this account as more data are required for these than the authors currently have available.
Xylopia ferruginea group
- The Xylopia ferruginea group is characterised by stilt roots, relatively long (5-19 mm) flower pedicels, a flat receptacle lacking a staminal cone (Fig. 2K ), flat narrowly oblong stamens with a tongue-shaped apex to the anther connective (Fig. 2J ), stigmas studded with small papillae (Fig. 2I ), and rugose seeds (Fig. 2C-D ).
- Seeds in a single row, parallel to long axis of monocarp, 6-12 per monocarp, 7.2-8.8 mm long, 5.5-5.6 mm wide, 4.7-5.1 mm thick, ellipsoid, elliptic in cross section, dark brown, rugose, flattened or a little concave at micropylar end, rounded at chalazal end, raphe and antiraphe distinctly raised; aril and aril plate absent.
- The bulk of the Sarawak and Brunei collections have come from either lowland peat swamp forest or heath forest (terminology following Saw, 2010) .
- These features are frequent in Sumatran specimens of Xylopia ferruginea s.s., which in general have larger and broader leaves than those of Peninsular Malaysian and Bornean plants, as well as a tendency toward a subcordate rather than truncate leaf base.
- The leaves are retuse at the apex and broadly cuneate and decurrent at the base.
Xylopia malayana group
- Species of the Xylopia malayana group are distinctive and well circumscribed with the exception of X. elliptica and X. malayana.
- The protologue, reproduced verbatim below, shows that the diagnosis emphasised the glabrous branches, the small elliptic, obtuse, membranous, glabrous leaves and the solitary flowers: 14.
- X. elliptica, Maingay mss.; branches glabrous, leaves small elliptic obtuse membranous glabrous, tip rounded, nerves faint reticulate, flowers small solitary erect pubescent, sepals subacute united to the middle, ovaries 1-3.
- Ridley (1922) subsequently maintained King's concept of the species intact.
- Restricted to a small area of southern Thailand and northwestern Peninsular Malaysia.
- All localities are in lowland evergreen forest.
- Flowers in July and August, fruit collected in July.
Local name. Kerangi lotong (Kedah: Awang 42444).
- The species is named for its unusually flattened and beanlike monocarps.
- Twigs dark brown to brownish grey, eventually lenticellate, glabrous or finely but sparsely pubescent and soon glabrate; double-branching occasional.
- Material of this species is usually identified in herbarium collections as Xylopia malayana, but X. ngii differs consistently from that species in its smaller (2-2.9 mm long) sepals sparsely covered with pale brown pubescence and the longer (13.5-34.2 mm) and narrower (1-1.6 mm wide at the midpoint) outer petals.
- The leaf blades are relatively small and oblong, often with a blotchy mottled appearance to the adaxial leaf blade surface when dried.
- Malaysia, Negeri Sembilan, Kuala Pilah, Pasoh F.R., Compt, also known as -TYPE.
- To confuse things further, this specimen was identified in turn as both Xylopia elliptica and X. malayana in the same publication by Corner (1978) .
- Six species are widespread across the Malay Peninsula, Sumatra and Borneo: Xylopia caudata Wall. ex Hook.f. & Thomson, X. ferruginea, X. fusca, X. malayana, X. ngii and X. sumatrana.
- Two species are shared between the Malay Peninsula and Borneo: Xylopia erythrodactyla and X. magna.
- Several species are large trees more than 40 meters in height, and this, coupled with sparseness of individuals in populations, may cause them to be overlooked.
- This explanation accords well with the extraordinary diversity of the genus found at sites such as the Pasoh Reserve, where in 2014 the authors verified the occurrence of seven Xylopia species in or near the Pasoh permanent 50-hectare research plot (Manokaran et al., 1992) .
- The authors results make clear, however, that further collecting and taxonomic analysis of the Malay Peninsula flora is still critically needed.
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Cites background from "A contribution to the systematics o..."
...This section is represented by 34 species in tropical Africa (Johnson & Murray 2018), 23 species on Madagascar, and c. 40 species in Southeast Asia. noteS Many of the sect....
...Variation in climatic conditions in South and Southeast Asia from the early Miocene onward (Morley 2018), would, however, have permitted intermittent migration of Xylopia eastward, with the genus ultimately reaching New Caledonia and Fiji by long-distance dispersal (Johnson et al. 2013)....
...Rugosperma D.M. Johnson & N.A. Murray (Asia), sect....
...In conclusion, Madagascar may have played a role in the dispersal of the Stenoxylopia clade into Asia, but there is no current evidence, morphological, fossil, or molecular, to suggest that the sect....
...Densely lenticellate oblong woody monocarps are unique among Madagascar Xylopia species, and rare in the genus, although this fruit morphology is known in species such as X. hypolampra in Africa (Johnson & Murray 2018) and X. ngii in Asia (Johnson & Murray 2015)....
"A contribution to the systematics o..." refers background in this paper
...The detached fruit on the sheet of KEP 20309 does not look like a fruit of Annonaceae, Sinclair’s determination of the specimen notwithstanding, but the leaves of the collection possibly represent this species. Turner (2011) designated the specimens K000574709 and K000574712 at K as lectotypes of the name Xylopia elliptica....
...The Annonaceae, a flowering plant family of 2500 species, including the economically important soursop, custard apple and ylang-ylang, is widespread across the tropics. The family is most diverse, and ecologically most significant, in tropical Asia, where it is represented by c. 40 genera and 800 species. In southeastern Asia it is one of the dominant families in lowland wet forests. Corlett & Turner (1997) determined that Annonaceae ranked fourth in species-richness among flowering plant families in Singapore; Appanah et al....
...Hand-written descriptive notes that are incorporated into the protologue are present on K000574709, and it is therefore designated as a second-step lectotype as permitted by Article 9.17 of the ICN (McNeill et al., 2012)....