Goniothalamus flagellistylus Tagane & V. S. Dang (Annonaceae), a new species from Mt. Hon Ba, Vietnam

Abstract A new species, Goniothalamus flagellistylus Tagane & V. S. Dang, sp. nov. from Hon Ba Nature Reserve in Khanh Hoa Province, South Vietnam is described and illustrated. This species is most similar to Goniothalamus tortilipetalus M.R.Hend., but distinct in having 308–336 stamens (vs. ca. 170–260) and ca.120 carpels (vs. ca. 50–100) per flower, and Stigma and pseudostyles ca.8.5 mm (vs. 4–4.5 mm) long.


Introduction
Th e genus Goniothalamus (Blume) Hook. f. & Th omson, with more than 130 species (Nakkhuntod et al. 2009, Tang et al. 2013, is one of the largest genera in the Annonaceae family. Th e species is characterized by mostly solitary, axillary and pendent fl owers, two whorls of petals with inner petals smaller than the outer ones, the inner petals connivent and forming a distinctive dome over the stamens and carpels acting as a pollination chamber and stamens having apical connectives. Most species of Goniothalamus are distributed in lowland evergreen rain forests in Southeast Asia, extending from India to Australia, also in New Caledonia (Jessup 1986, Mat-Salleh 2001, Saunders 2002, Saunders 2003, Kundu 2006, Saunders and Munzinger 2007, Saunders and Chalermglin 2008, Turner and Saunders 2008 (Finet and Gagnepain 1907, Hô 1999, Bân 2000.
During the botanical survey of Hon Ba Nature Reserve in South Vietnam, we encountered an undescribed species of Goniothalamus in Mt. Hon Ba at 400 m elevation. We here describe and illustrate this new species, Goniothalamus fl agellistylus Tagane & V. S. Dang, sp. nov.

Morphological observations
In order to verify the validity of this new species we undertook a thorough literature review, consulted specimens from the following herbaria FU, BKF, KYO, MBK and VNM, as well as online digitized plant specimens (e.g. JSTOR Global Plants).
Th e thickness of leaves, sepals and petals was measured using a digital caliper (Absolute Digimatic 547-401, Mitutoyo, Japan, resolution 0.001 mm).
Phenology. Mature fl owers and fruits were collected in July and November, respectively.
Etymology. Th e specifi c epithet is in reference to its fl exuous styles which is too long to insert straight in the pollination chamber that formed by the inner petals.

GeneBank accession No. Tagane et al. V1497: LC010815 (rbcL), LC010816 (matK).
Similar species. Goniothalamus fl agellistylus is morphologically similar to G. calvicarpus Craib, G. griffi thii Hook.f. & Th omson, and G. tortilipetalus, all of which form a monophyletic group (Nakkuntod et al. 2009) and are characterized by relatively large sepals with distinct veins and stamens with long apiculate connectives (Saunders and Chalermglin 2008). Among the three species, G. fl agellistylus is most similar to G. tortilipetalus, which is distributed in the Malay Peninsula, in having more than 200 stamens and more than 50 carpels. In fact, Th e BLAST similarity search based on the matK sequence of G. fl agellistylus resulted in homology as high as 734/736 bp with the sequence of G. tortilipetalus (GeneBank accession no. EU715081) in the DNA database. However, as described in the diagnosis above, the two species can be easily distinguished by the number of stamens and carpels per fl ower, and style length (Table 1). Also, G. fl agellistylus is diff erent from G. tortilipetalus in that fl owers arise not only from the main trunk but also from the older branches as in G. calvicarpus and G. griffi thii (Saunders and Chalermglin 2008).
Conservation status. Data defi cient. Goniothalamus fl agellistylus is known from a single population, including only six individuals: only one produces fl owers/fruits while the others are just saplings. Th is situation satisfi es the CR (critically endangered) status in criterion D of IUCN Red List Categories (IUCN 2014). However, more individuals could be found if neighboring areas are more thoroughly surveyed. Th us, we regard the conservation status as DD. In Mt. Hon Ba, large areas of primary evergreen forest below 300-400 m elevation had been cleared or selectively logged before the Hon Ba Nature Reserve established, and it is likely that some habitats of this species were lost. Th e forest habitat where we found G. fl agellistylus remains less disturbed under a lower level of logging activities probably because of its landform of the steep slope near the rapid river. Th e forest in this Nature Reserve is currently protected well from anthropogenic activities, and recovering better and better. Th e current data available are not enough for a risk evaluation, we therefore need special attention to the individuals/populations of G. fl agellistylus and its distribution.