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| Laobambos calcareus Haev., Lamxay & D.Z.Li, in Haevermans, Mantuano, Zhou, Lamxay, Haevermans, Blanc et Li, 2020. |
Abstract
Lush jungle flagship species, woody bamboos (Poaceae–Bambusoideae) are famed for their synchronous flowering as well as the extensive “bamboo forests” some species can form in tropical or temperate environments. In portions of their natural distribution, Bambusoideae members developed various adaptations to seasonality in environmental parameters, such as frost or seasonal drought. A new taxon, Laobambos calcareus, described here, is extremely novel in showing the first documented case of succulence in bamboos, with its ability to seasonally vary the volume of its stem depending on the quantity of water stored. Anatomical studies presented in this paper document this specificity at the cellular level. Though no flowers or fruits are known yet, unique morphological characteristics along with an investigation of its phylogenetic affinities using molecular data show that this new taxon should belong to a new genus herein described.
Keywords: Bambusinae, desiccation tolerance, genetic resources, xerophyte
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| Laobambos calcareus A Adult plant in habitat at the type locality during rainy season B detail of foliage leaves C detail of the waxy marks on fresh inflated culms, revealing the ridges present on the dried-state culm during the dormant period D detail of a node and a branch complement E view of base of the clump showing the greenish inflated fresh live culms, along with ridged dehydrated brown dead culms. (Photo credit Thomas Haevermans 05/2012). |
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| Laobambos calcareus. A Plant in habitat, growing in karst crevices typically along with Euphorbia antiquorum L. and Dracaena cochinchinensis (Lour.) S.C.Chen B leaf complement C plant in dormant state, rhizome leaves removed to show the structure D rhizome with year+1 shoot cross-section, and young shoots E petiole insertion with inner and outer ligules (view from below) F culm sheath, ventral view. Scale bars: 1 m (A); 2 cm (B); 5 cm (C, D); 2 mm (E); 1 cm (F). (Illustration credit Agathe Haevermans). |
Laobambos Haev., Lamxay & D.Z.Li, gen. nov.
Type species: Laobambos calcareus Haev., Lamxay & D.Z.Li.
Laobambos calcareus Haev., Lamxay & D.Z.Li, sp. nov.
Diagnosis: Similar to Bonia saxatilis var. solida in habit but differs in its succulent culms, persistent culm-sheaths, the unequal structure of its internode pattern, and the absence of culm leaf blade, auricles, or oral setae.
The generic name indicates that the new taxon is restricted to Laos, and the specific epithet emphasizes that the species is restricted to bare karstic crevices.
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| Scheme detailing Laobambos calcareus culm architecture illustrating the much elongated first internode, alternate branching with branch diameter matching the diameter of adjacent culm segment, and length of branches not exceeding the total length of the culm. (Illustration: Agathe Haevermans). |
Conclusion:
DNA sequences comparison informs us that this unique karst-restricted desiccation tolerant bamboo taxon is related to Neomicrocalamus and Temochloa (Fig. 5). However, no morphological characters unite it to these taxa and thus provides no justification for describing it as a species in one of these two sister genera. We decided to accommodate this species in a new genus to take into account its unique morphology and DNA-based phylogenetic relationships. Further work is needed as no other specimens (fertile or not) have been found in local and international herbaria such as the Paris herbarium (P), which holds a very large representative collection of bamboo specimens from this area. While its formal conservation status cannot be assessed for now due to data deficiency (it is thus tentatively rated Data Deficient), this taxon appears rare and quite restricted in range and habitat as only one population has been located by us or collaborators and thus likely belongs to one of the IUCN threat categories. Extensive fieldwork is required to try to locate other populations of this taxon as well as to collect flowering material if ever possible. Anatomical and developmental studies based on live plants are also necessary to document and understand the water storage cycle in this taxon and determine its abilities and limits in terms of desiccation tolerance. Being a wild relative of economically important tropical bamboos, further research into the adaptations of Laobambos toward desiccation tolerance may bring further breeding possibilities and genetic resources for commercial bamboo growers in seasonally dry areas hit by climate change.
Thomas Haevermans, Dulce Mantuano, Meng-Yuan Zhou, Vichith Lamxay, Agathe Haevermans, Patrick Blanc and De-Zhu Li. 2020. Discovery of the First Succulent Bamboo (Poaceae, Bambusoideae) in A New Genus from Laos’ Karst Areas, with A Unique Adaptation to Seasonal Drought. PhytoKeys. 156: 125-137. DOI: 10.3897/phytokeys.156.51636
