Gigantochloa glabrata (Poaceae, Bambusoideae), a new bamboo species from Yunnan, China

Abstract Gigantochloa glabrata N. H. Xia & Y. Zeng ex D. Z. Li & Z. C. Xu, sp. nov., a new species of paleotropical woody bamboo has been described and illustrated from Yunnan, China. The new species is morphologically similar to G. albociliata and G. levis, but differs from them by having erect culm sheath blades; culm sheath ligules 4–6 mm high, truncate, denticulate; and with a ring of white tomentum on the intranode and below the node. The new species was mistakenly identified as Gigantochloa albociliata in the Flora of China and was recognised with description of the vegetative characters in 2014, but it was not effectively published. Here, we designate a complete specimen with inflorescence as the type and describe it in accordance with the Code.


Introduction
Gigantochloa Kurz ex Munro was published as a new genus by Kurz (1864) without any detailed description. Munro described the morphological characters of this genus and validated the publication (Munro 1868). Currently, there are more than 60 species recognised in Gigantochloa from all over the world, which are distributed in the tropical lowlands of Southeast Asia (Holttum 1958;Widjaja 1987;Vorontsova et al. 2016), with seven species recorded in China (Li et al. 2006;Zeng et al. 2014). Species of Gigantochloa are characterised by their pseudospikelets clustered at each flowering branch node, oblong or linear, each with 2-4 florets and one terminal imperfect floret consisting only of an empty lemma, rhachilla internodes obscure, paleas 2-keeled, the keels and the inflexed margins long-ciliate above; lodicules often absent; stamens six, the filaments connated into a hyaline tube which can elongate and become membranous, with anthers apiculate with minutely hispidulous tips (Munro 1868). Since its eastablishment, many bamboo taxonomists have considered it as a "good genus", based on morphological characteristics (Kurz 1875(Kurz , 1876Holttum 1958;Clayton and Renvoize 1986;Widjaja 1987).
As a genus of paleotropical woody bamboo, Gigantochloa belongs to the subtribe Bambusinae Presl (BPG 2012). It was included in the Bambusa-Dendrocalamus-Gigantochloa (BDG) complex, together with Bambusa Schreber, Dendrocalamus Nees and closely-related small genera (Goh et al. 2010;Goh et al. 2013;Zhou et al. 2017). Morphologically, Bambusa can be distinguished from Gigantochloa by its conspicuous auricles and florets falling separately. Dendrocalamus can be recognised by its free filaments. In our recent molecular phylogenetic study, Gigantochloa was well resolved as a monophyletic group (Liu et al. 2020).
By studying the species of Gigantochloa from the Yunnan-Myanmar-Thailand floristic region, we found that G. albociliata, recorded in Flora Reipublicae Popularis Sinicae (Keng and Wang 1996) and Flora of China (Li et al. 2006) is not truly G. albociliata (Munro) Kurz. Accordingly, a new species needs to be described to clarify this long-existing taxonomic problem.

Materials and methods
All measurements and observation of morphological characters were conducted, based on the specimens at the Herbarium of the Kunming Institute of Botany (KUN), Herbarium of the Xishuangbanna Tropical Botanical Garden (HITBC) and the Herbarium of the South China Botanical Garden (IBSC), as well as the photos of living individuals taken from living collections of the Xishuangbanna Tropical Botanical Garden in the summer of 2019. Pseudospikelets were dissected under an OLYMPUS DP80 digital microscope at Germplasm Bank of Wild Species of the Kunming Institute of Botany. Morphological comparisons with closely-related species (G. albociliata and G. levis (Blanco) Merr. (Blanco 1837;Merrill 1916)) were based on characters recorded in literature and on the type specimens. The morphological terminology follows McClure (McClure 1966).

Taxonomy
Gigantochloa albociliata (Munro) Kurz was first recorded in Yunnan, southwest China by Sun (1984) and it was included in Flora Reipublicae Popularis Sinicae (Keng and Wang 1996), Flora of China (Li et al. 2006) and the Flora of China Illustrations (Zhang 2007). However, the description and illustrations of the Flora of China and the protologues of G. albociliata did not match. When we checked the specimens of Gigantochloa at the HITBC in 2019, we noticed that the inflorescence specimen, collected by K. H. He (no. C130051) in 2007, was identical with "G. albociliata" in the sense of Flora of China. We collected inflorescence material in the living collection of the Xishuangbanna Tropical Botanical Garden again in August 2019. After comparison with specimens of G. albociliata and other closely-related Gigantochloa species, we could not place it within any described species of Gigantochloa. In the meantime, we noticed that this species was recognised by Zeng (2014) as a new species with description of the vegetative characters. Zeng's new name is available via the International Plant Names Index (IPNI 2020); however, according to the Code (Turland et al. 2018), it was not effectively published, because it appeared only in a thesis submitted to a university for the purpose of obtaining a degree, with neither an ISBN number nor statement of the name of the printer, publisher or distributor in the original printed version (Art. 30.9). Here, we added reproductive characters and a detailed morphological comparison to validate the new species as G. glabrata N. H. Xia & Y. Zeng. We designate a complete specimen with an inflorescence as the type and describe it in accordance with the Code.
Phenology. New shoots May to August. Distribution and habitat. Gigantochloa glabrata is cultivated at the Bamboo Garden, XTBG, introduced from Mengyang Town, Jinghong City, Yunnan, China in 1978with XTBG accession no. 00.1978. However, we could not find it over a field survey in Mengyang area in 2019.
Etymology. The specific epithet refers to the culm sheath covered with sparsely deciduous hairs.

Discussion
Xishuangbanna is a hotspot of biodiversity in the world and it is also the northern edge of the distribution of Gigantochloa. Our discovery not only increases the bamboo species diversity of this area, but also solves the problem of erroneous identifications and citations of G. albociliata in Chinese botanical literature for two decades, including the authoritative Flora Reipublicae Popularis Sinicae and Flora of China, as well as provincial and regional Floras.