Saturday, May 12, 2018

[Botany • 2018] A New Annonaceae Genus, Wuodendron, Provides Support for A post-Boreotropical Origin of the Asian-Neotropical Disjunction in the tribe Miliuseae

Wuodendron  B.Xue, Y.H.Tan & Chaowasku 
Wuodendron praecox  
(Hook.f. & Thomson) B.Xue, Y.H.Tan & X.L.Hou

in Xue, Tan, Thomas, Chaowasku, Hou & Saunders, 2018. 


Recent molecular and morphological studies have clarified generic circumscriptions in Annonaceae tribe Miliuseae and resulted in the segregation of disparate elements from the previously highly polyphyletic genus Polyalthia s.l. Several names in Polyalthia nevertheless remain unresolved, awaiting assignment to specific genera, including Polyalthia litseifolia. Phylogenetic analyses of seven chloroplast regions (atpB-rbcL, matK, ndhF, psbA-trnH, rbcL, trnL-F, ycf1; ca. 8.3 kb, 116 accessions, including representatives of all currently accepted genera in subfamily Malmeoideae) unambiguously placed Polyalthia litseifolia in a clade with three accessions from Thailand, which have previously been shown to represent an undescribed genus sister to the Neotropical clade (Desmopsis, Sapranthus, Stenanona, Tridimeris) in the predominantly Asian tribe Miliuseae. The collective clade is sister to Meiogyne. Polyalthia litseifolia shares several diagnostic characters with most species in the Neotropical genera and Meiogyne, including: petals that are similar in shape and size in both whorls; multiple ovules per ovary in one or two rows; and lamelliform endosperm ruminations. It is distinct in being deciduous, bearing subpetiolar buds and having inflorescences growing from the leaf scar of the dropped leaves. Morphological comparisons and phylogenetic analyses corroborate its recognition as a new genus, which is formally described and illustrated here as Wuodendron. Polyalthia litseifolia is furthermore found to be conspecific with Desmos praecox, and the latter name is used as the basis for the name of the type. Molecular divergence time estimates under an uncorrelated lognormal relaxed clock place the Wuodendron-Neotropical clade split within the Miocene (ca. 14–12 Ma), highlighting the importance of post-boreotropical dispersal and vicariance in shaping intercontinental tropical disjunctions in Annonaceae. 

Keywords: Annonaceae; deciduous; Desmos praecox; intercontinental tropical disjunction; new genus; Polyalthia litseifolia


Fig. 3. Morphology of Wuodendron praecox comb. nov. (= Polyalthia litseifolia).
A, Trunk, showing grayish bark with lenticels; B, Young leaves; C, Close-up of the adaxial surface of fresh leaf, showing glands; D, Close-up of the adaxial surface of dried leaf, showing glands; E, Subpetiolar bud; F, Swollen base of the petiole that encloses the bud; G, Inflorescence and new leaf growing from the axil of the dropped leaf; H, Dissected flower, showing three sepals, three outer petals, three inner petals and the pedicel (Y.H. Tan 12258, HITBC); I, Young fruit, showing the infructescence and the branchlet growing from the same axil (Nakorn-Thiemchan NTC23, CMUB); J, Mature fruit; K, Monocarps, showing slight constrictions between seeds, and multiple seeds in one row in one monocarp (Y.H. Tan 10946, HITBC); L, Cylindrical seeds, showing the distinct circumferential groove; and the longitudinal section of the seed, showing lamelliform endosperm rumination (Y.H. Tan 10946, HITBC).

Following detailed examination of protologues and specimens, we did not find any evidence to uphold both the poorly known Desmos praecox and Polyalthia litseifolia as distinct species. The basionym Unona praecox antedates P. litseifolia and hence its specific epithet has priority.

Wuodendron B.Xue, Y.H.Tan & Chaowasku, gen. nov.
– Type: W. praecox (Hook.f. & Thomson) B.Xue, Y.H.Tan & X.L.Hou 
(≡ Unona praecox Hook.f. & Thomson).

Diagnosis. – Wuodendron resembles the closely related genera Desmopsis, Meiogyne, Sapranthus, Stenanona and Tridimeris, with which it shares petals that are more or less similar in shape and size in both whorls and the multi-ovuled ovaries; Wuodendron differs, however, in having subpetiolar buds and inflorescences growing from the axils of the circular leaf scars where old leaves have fallen.

Distribution. – A single species, known from China, India, Myanmar, Thailand, and Vietnam; as well as in Cambodia and Laos (Hong Wang, pers. comm.).

Etymology. – Named after Wu Zhengyi (= C.Y. Wu, of the Kunming Institute of Botany, Chinese Academy of Sciences), who proposed the name of Polyalthia litseifolia, in honor of his great contribution to plant taxonomy.

Wuodendron praecox (Hook.f. & Thomson) B.Xue, Y.H.Tan & X.L.Hou, comb. nov.

≡ Unona praecox Hook.f. & Thomson, Fl. Ind. 1: 136. 1855 ≡ Desmos praecox (Hook.f. & Thomson) Saff. in Bull. Torrey Bot. Club 1912: 39. 1912 – Lectotype (designated by Turner in Nordic J. Bot. 33: 265. 2015): INDIA. Assam: Mikir Hills, Feb, C.J. Simons 156 (K barcode K000190045, digital image!).
Polyalthia litseifolia C.Y.Wu ex P.T.Li in Acta Phytotax. Sin. 14: 110. 1976 – Holotype: CHINA. Yunnan: Jinghong, elevation 1100 m, 24 Apr 1957, Sino-Russia Exped. 9488 (KUN barcode 0046659!; isotype: PE barcode 00934528!). Chinese name. – mu jiang ye zheng yi mu (木姜叶征镒木). Description. – Large trees 15–40 m tall, ca. 30–40(–80)




 Bine Xue, Yun-Hong Tan, Daniel C. Thomas, Tanawat Chaowasku, Xue-Liang Hou and Richard M.K. Saunders. 2018. A New Annonaceae Genus, Wuodendron, Provides Support for A post-Boreotropical Origin of the Asian-Neotropical Disjunction in the tribe Miliuseae.  TAXON67(2); 250–266. DOI: 10.12705/672.2