Leoheo Chaowasku

Chaowasku, Tanawat, Damthongdee, Anissara, Jongsook, Hathaichanok, Ngo, Dung T., Le, Hung T., Tran, Duc M. & Suddee, Somran, 2018, Enlarging the monotypic Monocarpieae (Annonaceae, Malmeoideae): recognition of a second genus from Vietnam informed by morphology and molecular phylogenetics, Candollea 73 (2), pp. 261-275: 264-268

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Leoheo Chaowasku

gen. nov.

Leoheo Chaowasku   , gen. nov.

Typus: Leoheo domatiophorus Chaowasku, D.T. Ngo & H.T. Le.  

Medium-sized to large trees; indumentum of simple hairs; intramarginal leaf veins absent, tertiary leaf venation percurrent; inflorescences 1- or few-flowered, axillary; bracts present; flowers bisexual, both petal whorls of ± equal size; stamens 70– 76, connective truncate and dilated, covering thecae; carpels 3– 4 per flower, free in flower and fruit; stigmas ± peltate and lobed; ovules many and arranged in two rows, placentation lateral; monocarps subsessile, cylindrical, monocarp abscission basal, pericarp thick and hardened when dry; aril absent; endosperm ruminations spiniform.

Etymology. – The generic epithet Leoheo   is from the local Vietnamese name of “Lèo Heo” for this plant and is designated as a masculine noun of nominative singular in third declension with genitive singular “Leoheonis”.

Notes. – The principal morphological differences between Leoheo   and Monocarpia   are highlighted in Table 1 View Table 1 . Furthermore, in view of molecular phylogenetics, the genera Leoheo   and Monocarpia   each is characterizable not only by nucleotide substitutions, but also by an indel structure in the psbA-trnH intergenic spacer for Leoheo   and another indel structure in the trnL-trnF intergenic spacer for Monocarpia   . Although the other two species of Monocarpia   , M. borneensis Mols & Kessler   and M. kalimantanensis Kessler   , have not been included in the present molecular phylogenetic analyses due to the failure in DNA amplification, their morphologies (e.g. Fig. 2A, 3B View Fig. 1. – 50 ) substantially coincide with those of M. euneura Miq.   and M. maingayi   (Hook. f. & Thomson) I.M. Turner ( Fig. 2B View Fig. 1. – 50 ; TURNER, 2012), hence we are convinced that such two missing species (both or any of them) will not retrieve as the sister group of Leoheo   or the Leoheo-Monocarpia clade.

It is noteworthy that each of the axillary inflorescences of the genus Leoheo   often contains leaf-like bract(s) at the top of peduncle ( Fig. 3A, 6 View Fig. 1. – 50 ), probably this feature is a transition to the terminal inflorescences characteristic for the genus Monocarpia   ( Fig. 3B View Fig. 1. – 50 ). The presence of domatia on the lower leaf surface is a rare phenomenon in Annonaceae   . It occurs only in a limited number of genera and species, for examples, Annona   L. ( VAN DEN BOS et al., 1989), Dendrokingstonia Rauschert   ( CHAOWASKU et al., 2012b), Huberantha Chaowasku   ( CHAOWASKU et al., 2012a), Mitrephora (Blume) Hook.   f. & Thomson ( WEERASOORIYA & SAUNDERS, 2010), and Tridimeris Baill.   ( ORTIZ-RODRIGUEZ et al., 2016). Of these genera, the hairy type of domatium similar to that of Leoheo   ( Fig. 4A View Fig. 1. – 50 ) can be found in Annona   , Huberantha   , and Mitrephora   ( CHAOWASKU et al., 2012a).

The well-supported sister relationship of Fenerivieae   and Maasieae   is reported herein for the first time ( Fig. 1 View Fig. 1. – 50 ). The two tribes share a number of features, e.g., axillary inflorescences, generally one ovule per ovary, and spiniform endosperm ruminations ( MOLS et al., 2008; SAUNDERS et al., 2011). Their possible closest relationships were previously discussed ( SCHATZ & LE THOMAS, 1990; SAUNDERS et al., 2011).

The tribes Phoenicantheae, Monocarpieae   , Dendrokingstonieae   , and Miliuseae   constitute a strongly supported clade substantially composed of Asian-Pacific species. The fact that the Sri Lankan endemic tribe Phoenicantheae is the sister group of the remainder of this clade coupled with the restricted distribution of the tribes Monocarpieae   and Dendrokingstonieae   might have some biogeographic implication, especially on the geographic origin of Miliuseae   , the most diverse tribe of Malmeoideae   ( CHATROU et al., 2012), but it is currently not possible to perform an in-depth biogeographic analysis because there are still unignorable phylogenetic uncertainties, especially the unsupported sister relationships of Dendrokingstonieae   and Miliuseae   , as well as of Malmeeae   and a clade composed of Fenerivieae   and Maasieae   ( Fig. 1 View Fig. 1. – 50 ). So far, no macromorphological features have yet been found to be synapomorphic for the Phoenicantheae-Monocarpieae-Dendrokingstonieae- Miliuseae   clade. Nevertheless, some palynological correlations have been observed, i.e., any taxa of Malmeoideae   recovered outside Miliuseae   possess monosulcate pollen ( CHAOWASKU et al., 2012b, 2014). Currently the pollen data of Phoenicanthus   and Leoheo   are unavailable, but they are anticipated to exhibit monosulcate pollen based on such correlations. In addition, it is worthwhile to note that Phoenicantheae, Monocarpieae   , and Dendrokingstonieae   all possess a highly reduced carpel number to 1–4 per flower ( HUBER, 1985; CHAOWASKU et al., 2012b). It is likely that the reduction in carpel number per flower is the ancestral trait of the Phoenicantheae-Monocarpieae- Dendrokingstonieae-Miliuseae clade. Table 2 View Table 2 compares the important macromorphological and pollen morphological characters of the amended Monocarpieae   and the other three closely related tribes: Phoenicantheae, Dendrokingstonieae   , and Miliuseae   .

Monocarpia   , the sister group of Leoheo   , occurs in southern Thailand, Peninsular Malaysia, Sumatra, and Borneo ( TURNER, 2012); the shortest distance of the two genera is about 1300 km away. This disjunct distribution pattern is, however, not unprecedented. In Phaeanthus Hook.   f. & Thomson ( Malmeoideae   , Miliuseae   ; CHATROU et al., 2012), P. vietnamensis Bân   is the only species occurring in Indochinese Peninsula; the remaining species occur in southern Thailand Provinces bordering Malaysia ( GARDNER et al., 2015), Malay Peninsula to the Philippines and New Guinea ( MOLS & KESSLER, 2000a). In Neo-uvaria Airy Shaw   ( Malmeoideae   , Miliuseae   ; CHATROU et al., 2012), the recently described N. laosensis Tagane & Soulad.   hitherto endemic to central Laos ( TAGANE et al., 2018) is the only species disjunctly occurring north of Peninsular Thailand and

Malaysia, the nearest area where three other species of Neouvaria   can be found ( CHAOWASKU et al., 2011). Additionally, in Disepalum Hook.   f. ( Annonoideae   , Annoneae   ; CHATROU et al., 2012) subg. Enicosanthellum (Bân) P.S. Li, D.C. Thomas & R.M.K. Saunders   , a clade composed of two particular species: D. petelotii (Merr.) D.M. Johnson   and D. plagioneurum (Diels) D.M. Johnson   , both occurring in China and Vietnam (and Laos for the former; JOHNSON, 1989) is the sister group of D. pulchrum (King) J. Sinclair   ( LI et al., 2015, 2017) which can only be found in southern Thailand Provinces bordering Malaysia ( CHAMCHUMROON et al., 2017) and Malay Peninsula ( JOHNSON, 1989). It is interesting to understand the plausible biogeographic scenarios and other biotic/abiotic factors shaping the mentioned disjunct distribution pattern within Southeast Asia.

Table 1. – Principal morphological differences between Leoheo Chaowasku and Monocarpia Miq.

Characters Leoheo   Monocarpia  
Intramarginal leaf veins Absent Present
Domatia on lower leaf surface Present Absent
Inflorescence position Axillary Terminal
Monocarp surface With longitudinal ridges Without longitudinal ridges
Monocarp base Contracted into a short and stout stipe Not contracted into a stipe

Table 1. – Principal morphological differences between Leoheo Chaowasku   and Monocarpia Miq.  

Table 2. – Comparisons of important macromorphological and pollen morphological features of four closely related tribes in Malmeoideae.

Characters Phoenicantheae Monocarpieae   Dendrokingstonieae   Miliuseae  
Tertiary leaf venation Reticulate Percurrent Percurrent Reticulate to percurrent
Inflorescence position Axillary or terminal Axillary or terminal Axillary Axillary or terminal
Stamen number per flower 6 or 9 35–76 9–56 3 to ≥ 200
Stamen connective tissue With a minute prolongation, not covering thecae Truncate and dilated, covering thecae Truncate and dilated, covering thecae Without an apical prolongation; or with a minute prolongation, not covering thecae; or truncate and dilated, covering thecae; or +/– truncate, not covering thecae
Carpel number per flower 1–3 1–4 1–2 1 to ≥ 70
Pollen apertural system Monosulcate Monosulcate Monosulcate Cryptoaperturate/disulculate

Table 2. – Comparisons of important macromorphological and pollen morphological features of four closely related tribes in Malmeoideae   .