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A new species of Petrocosmea (Gesneriaceae) from Myanmar

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The new species Petrocosmea villosa D.J.Middleton from Shan State, Myanmar is described. It is most similar to Petrocosmea kerrii Craib, P. crinita (W.T.Wang) Z.J.Qiu and P. heterophylla B.L.Burtt in Petrocosmea sect. Deinanthera but differs particularly in inflorescence structure, inflorescence indumentum and in the long calyx lobes.
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Gardens’ Bulletin Singapore 73(2): 457–460. 2021
doi: 10.26492/gbs73(2).2021-14
A new species of Petrocosmea (Gesneriaceae)
from Myanmar
D.J. Middleton1, Thant Shin2 & Y. Baba3
1Singapore Botanic Gardens, National Parks Board,
1 Cluny Road, 259569 Singapore
david_middleton@nparks.gov.sg
2Forest Research Institute, 15013 Yezin,
Zayarthiri Township, Naypyidaw, Myanmar
3Auckland War Memorial Museum Tāmaki Paenga Hira,
Private Bag 92018, Auckland 1142, New Zealand
ABSTRACT. The new species Petrocosmea villosa D.J.Middleton from Shan State, Myanmar
is described. It is most similar to Petrocosmea kerrii Craib, P. crinita (W.T.Wang) Z.J.Qiu
and P. heterophylla B.L.Burtt in Petrocosmea sect. Deinanthera but differs particularly in
inorescence structure, inorescence indumentum and in the long calyx lobes.
Keywords. Petrocosmea crinita, Petrocosmea heterophylla, Petrocosmea kerrii, Petrocosmea
sect. Deinanthera, Shan State
Introduction
The genus Petrocosmea Oliv. consists of between 47 species (Wen, 2019) and 55
species (GRC 2021, continuously updated) in southwestern China, northeastern India,
Myanmar, Thailand and Vietnam. Craib (1919) recognised two sections within the
genus based on the relative sizes of the upper and lower lips of the corolla. Wang
(1985) added a third section, Petrocosmea sect. Deinanthera W.T.Wang, to include
the species with the anthers constricted at the apex to form a short thick beak. Qiu
et al. (2015) suggested, however, that the existing sectional treatment of the genus
insufciently reects its morphological diversity and phylogeny.
A specimen, Baba et al. 103535, collected from Myanmar, Shan State, Lomkok
Mountain at 1106 m elevation, has the anther shape characteristic of Petrocosmea sect.
Deinanthera, which has about nine species altogether and which is most diverse in
nearby northern Thailand (Wang, 1985; Middleton & Triboun, 2010). It is not one of
the known species of this section so is here described as new.
Only two other species of Petrocosmea are currently recorded from Myanmar,
P. kerrii Craib and P. kingii (C.B.Clarke) Chatterjee (Kress et al., 2003), although it
would be surprising if P. bicolor D.J.Middleton & Triboun, P. formosa B.L.Burtt, P.
heterophylla B.L.Burtt, P. pubescens D.J.Middleton & Triboun and possibly even P.
umbelliformis B.L.Burtt were not also eventually to be found in the country given their
collection localities in Thailand close to the Myanmar border.
Gard. Bull. Singapore 73(2) 2021
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New species
Petrocosmea villosa D.J.Middleton, sp. nov.
Similar to Petrocosmea kerrii and P. crinita (W.T.Wang) Z.J.Qiu in the shape and
colour of the corolla but differs from both in having both sessile and petiolate leaves
(petiolate only in P. kerrii and P. crinita), longer calyx lobes (11–12 mm long in P.
villosa, 1.5–4 mm long in P. kerrii and P. crinita) and more owers in the inorescence
than P. kerrii (8–12 in P. villosa, 1–4 in P. kerrii). Also similar to Petrocosmea
heterophylla in having two types of leaves and in the shape and colour of the corolla
but differs in the sessile leaves being smaller (to 2 cm long in P. villosa, to 5.5 cm long
in P. heterophylla), the villous hairs in P. villosa (pubescent rather than villous in P.
heterophylla), inorescence more congested in P. villosa (lax in P. heterophylla), and
longer calyx lobes (11–12 mm long in P. villosa, 4.5–8 mm long in P. heterophylla).
– TYPE: Myanmar, Shan State, Taunggyi Township, Lomkok mountain and pagoda,
1106 m, 20°49′2.4″N 97°13′26.6″E, 20 September 2015, Y. Baba, K. Kertsawang, C.
Kilgour, S. Ruchisansakun, P. Srisanga, P.P. Hnin & Yo El 103535 (holotype MBK;
isotype RAF n.v.). (Fig. 1)
Rosulate herb with two types of leaves: a cluster of sessile leaves and long-petiolate
leaves. Sessile leaves few, c. 2 cm long, densely villous. Petiolate leaves: petioles 2.5–
8 cm long, densely pubescent; blades ovate, 1.9–13.2 × 1.1–6.6 cm, 1.4–2.1 times as
long as wide, base rounded to weakly cordate, apex acuminate, margin denticulate, 4–7
pairs of ascending secondary veins, pubescent above and beneath, more densely so on
venation. Inorescences few per plant, with 8–12 owers, 8–10 cm long, umbelliform
with owers crowded at apex, densely white villous throughout; peduncle 5.5–8 cm
long; pedicels 3–7.5 mm long. Calyx pale green, weakly 2-lipped, the lower 2 lobes
free, the upper 3 lobes fused at base for 2 mm, all lobes narrowly triangular, apices
caudate, margins crenulate towards apex, densely villous outside, glabrous inside;
lower lobes 12 × 2.1 mm, upper lobes 11–12 × 2.4–2.9 mm, lateral ones slightly
falcate. Corolla c. 1 cm long, tube short and limb spreading resulting in a at-faced
ower, white tinged yellow at base of upper lip, with orange-yellow markings at base
of lower lip, outside pubescent on lobes and with sessile glands, inside with short hairs
at throat and with sessile glands at base of upper lip; tube c. 3 mm long; limb 2-lipped;
upper lip 2-lobed, c. 7 mm long, lobes c. 7 × 7 mm, sinus between them c. 3.5 mm
deep; lower lip 3-lobed, c. 8.5 mm long, lateral lobes c. 5.5 × 6 mm, middle lobe c.
4 × 5 mm. Stamens inserted at base of corolla tube, anthers pressed face to face but
not coherent in rehydrated owers; laments c. 1 mm long, c. 1.1 mm wide; anthers
2, c. 4.7 × 2.5 mm, apical beak c. 1 mm long; staminodes 3, c. 0.7 mm long. Pistil c.
9.5 mm long, eglandular pubescent throughout; ovary c. 4 mm long; style and stigma
c. 5.5 mm long. Fruit a plagiocarpic capsule on elongated pedicels, 5.5–6 mm long.
Distribution. Only known from the type locality.
Ecology. Edge of evergreen forest on limestone karst.
459
Petrocosmea villosa, a new species from Myanmar
Fig. 1. Petrocosmea villosa D.J.Middleton. A. Flower front view. B. Flower side view. (Photo:
S. Ruchisansakun)
Gard. Bull. Singapore 73(2) 2021
460
Etymology. The specic epithet refers to the dense hair covering on the inorescence.
Provisional IUCN conservation assessment. Data Decient (DD) according to the
IUCN Red List Categories and Criteria (IUCN Standards and Petitions Committee,
2019). As it is currently only known from the type collection and its distribution and
population size are insufciently known, it is assessed here as DD. The collection
locality is not within a protected area but there is a pagoda near the collection locality,
affording protection from large scale destruction (such as mining).
ACKNOWLEDGEMENTS. We thank the collectors of the type and the collectors in turn
are grateful to Dr Nyi Nyi Kyaw, Director General, Forest Department, Ministry of Natural
Resources and Environmental Conservation for his continuous support for oristic research
in Myanmar. The eld work was conducted under an MoU between the Myanmar Forest
Department and Kochi Prefecture Makino Botanical Garden (MBK). The curatorial staff of the
herbarium at MBK are thanked for the loan of material to Singapore Botanic Gardens (SBG).
We thank Dr Saroj Ruchisansakun for the photographs used in Fig. 1.
References
Craib, W.G. (1919). Revision of Petrocosmea. Notes Roy. Bot. Gard. Edinburgh 111: 269–275.
GRC 2021 (continuously updated). Gesneriaceae Resource Centre. http://padme.rbge.org.uk/
GRC/. Royal Botanic Garden Edinburgh. Accessed 16 Aug. 2021.
IUCN Standards and Petitions Committee (2019). Guidelines for Using the IUCN Red List
Categories and Criteria. Version 14. Prepared by the Standards and Petitions Committee.
Available from: http://iucnredlist.org/documents/RedListGuidelines.pdf.
Kress, W.J., De Filipps, R.A., Farr, E. & Kyi, D.Y.Y. (2003). A checklist of the trees, shrubs,
herbs, and climbers of Myanmar. Contr. U.S. Natl. Herb. 45: 1–590.
Middleton, D.J. & Triboun, P. (2010). Two new species of Petrocosmea (Gesneriaceae). Thai
For. Bull., Bot. 38: 42–47.
Qiu, Z.J., Lu, Y.X., Li, C.Q., Dong, Y., Smith, J.F. & Wang, Z.Y. (2015). Origin and evolution
of Petrocosmea (Gesneriaceae) inferred from both DNA sequence and novel ndings in
morphology with a test of morphology-based hypotheses. BMC Pl. Biol. 15-167: 1–19.
Wang, W.T. (1985). The second revision of the genus Petrocosmea (Gesneriaceae). Acta Bot.
Yunnan. 7(1): 49–68.
Wen, F. (2019). Petrocosmea weiyigangii (Gesneriaceae), a new species from a limestone cave
in southern China. Gard. Bull. Singapore 71: 175–183.
... The color of the indumentum in most wild individuals of P. hsiwenii is usually red, which is also an obvious distinguishing feature. The division of groups of this genus has always been very difficult, and some scholars think the existing sectional treatment of the genus insufficiently reflects its morphological diversity and phylogeny (Middleton et al., 2021;Qiu and Liu, 2015). However, the boundaries of the genus have not changed after research based on molecular and morphological data, thus, the systematic taxonomy of this genus is worthy of further study (Qiu and Liu, 2015). ...
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Petrocosmea Oliver (Gesneriaceae) currently comprises 38 species with four non-nominate varieties, nearly all of which have been described solely from herbarium specimens. However, the dried specimens have obscured the full range of extremely diverse morphological variation that exists in the genus and has resulted in a poor subgeneric classification system that does not reflect the evolutionary history of this group. It is important to develop innovative methods to find new morphological traits and reexamine and reevaluate the traditionally used morphological data based on new hypothesis. In addition, Petrocosmea is a mid-sized genus but exhibits extreme diverse floral variants. This makes the genus of particular interest in addressing the question whether there are any key factors that is specifically associated with their evolution and diversification. Here we present the first phylogenetic analyses of the genus based on dense taxonomic sampling and multiple genes combined with a comprehensive morphological investigation. Maximum-parsimony, maximum likelihood and Bayesian analyses of molecular data from two nuclear DNA and six cpDNA regions support the monophyly of Petrocosmea and recover five major clades within the genus, which is strongly corroborated by the reconstruction of ancestral states for twelve new morphological characters directly observed from living material. Ancestral area reconstruction shows that its most common ancestor was likely located east and southeast of the Himalaya-Tibetan plateau. The origin of Petrocosmea from a potentially Raphiocarpus-like ancestor might have involved a series of morphological modifications from caulescent to acaulescent habit as well as from a tetrandrous flower with a long corolla-tube to a diandrous flower with a short corolla-tube, also evident in the vestigial caulescent habit and transitional floral form in clade A that is sister to the remainder of the genus. Among the five clades in Petrocosmea, the patterns of floral morphological differentiation are consistent with discontinuous lineage-associated morphotypes as a repeated adaptive response to alternative environments. Our results suggest that the lineage-specific morphological differentiations reflected in the upper lip, a functional organ for insect pollination, are likely adaptive responses to pollinator shifts. We further recognize that the floral morphological diversification in Petrocosmea involves several evolutionary phenomena, i.e. evolutionary successive specialization, reversals, parallel evolution, and convergent evolution, which are probably associated with adaptation to pollination against the background of heterogeneous abiotic and biotic environments in the eastern wing regions of Himalaya-Tibetan plateau.
Revision of Petrocosmea
  • W G Craib
Craib, W.G. (1919). Revision of Petrocosmea. Notes Roy. Bot. Gard. Edinburgh 111: 269-275. GRC 2021 (continuously updated). Gesneriaceae Resource Centre. http://padme.rbge.org.uk/ GRC/. Royal Botanic Garden Edinburgh. Accessed 16 Aug. 2021.
The second revision of the genus Petrocosmea (Gesneriaceae)
  • W T Wang
Wang, W.T. (1985). The second revision of the genus Petrocosmea (Gesneriaceae). Acta Bot. Yunnan. 7(1): 49-68.