Coleus Namuliensis and Coleus Caudatus (Lamiaceae): a New Species and a New Combination in the Afromontane Flora of Mozambique and Zimbabwe
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Blumea 62, 2017: 168–173 ISSN (Online) 2212-1676 www.ingentaconnect.com/content/nhn/blumea RESEARCH ARTICLE https://doi.org/10.3767/blumea.2017.62.03.02 Coleus namuliensis and Coleus caudatus (Lamiaceae): a new species and a new combination in the Afromontane flora of Mozambique and Zimbabwe E. Downes1, I. Darbyshire1,2 Key words Abstract The new species Coleus namuliensis (Lamiaceae) is described from the granite outcrops and grasslands of Mt Namuli in Zambezia Province of Mozambique. It has previously been confused with Plectranthus caudatus, endemic species a species that is restricted to the quartzite outcrops of the Chimanimani Mountains on the Mozambique-Zimbabwe IUCN conservation assessment border for which the new combination in Coleus is formalised in this paper. Other potential confusion species are taxonomy discussed and a rationale for applying the generic name Coleus rather than Plectranthus is provided. Despite their highly restricted ranges, C. namuliensis and C. caudatus are both considered to have a conservation status of Least Concern at present, although climate change may pose a longer-term threat to their survival. Published on 9 October 2017 INTRODUCTION 2006, Paton et al. 2009, 2013) were consulted to find any other potentially allied species, each of which were examined and Whilst preparing a conservation assessment for Plectranthus compared with the Namuli plants (see Table 1). It was concluded caudatus S.Moore, a species previously considered to be that the Namuli plants are a new species to science, appar- endemic to the quartzite outcrops of the Chimanimani Moun- ently restricted to that mountain, and the species is formally tains, three specimens were found in the Kew herbarium described below. named to this species but collected on the granite outcrops of Mt Namuli, some 650 km to the northeast of Chimanimani. Applying the correct generic name: Plectranthus vs Coleus These specimens were collected in 2007 during biodiversity Taken in a broad sense as per recent treatments of the genus surveys conducted in the mountains of Zambézia Province, (e.g., Paton et al. 2009, 2013), Plectranthus is a large genus northern Mozambique under a Darwin Initiative award. The with approximately 300 species in the Old World Tropics (Luk- treatment of Plectranthus L’Hér. for Flora Zambesiaca Lami- hoba et al. 2006, Paton et al. 2009). Morton (1962) was the aceae (Paton et al. 2013) had already been prepared by the earliest in the modern era, but not the first historically, to treat time these specimens were available for study at Kew and Coleus Lour. as congeneric with Plectranthus, although he did so they were not studied in detail or cited in the account. In maintain Solenostemon Thonn. as a distinct genus. Previously view of the marked disjunction in distribution and particularly they had been distinguished by Bentham (1832, 1848) on the the differing geology, it was considered likely that these two basis of free stamens in Plectranthus vs stamens fused into populations represented different taxa and so the Namuli plants a sheath in Coleus, but this was found to be an unreliable were examined in more detail by the current authors. These distinction (Morton 1962, Codd 1971, 1975, Pollard & Paton specimens share many superficial similarities with P. caudatus, 2001, Paton et al. 2009, 2013). Consequently, Coleus was including the fleshy habit and dense inflorescence spikes with subsumed into Plectranthus (Morton 1962, Codd 1971) as no a villose indumentum and, except for the differing substrate, clear differentiating characters were found. they are known from analogous environments, being found in rocky montane grassland. Indeed, using the treatment of Plec- However, recent molecular phylogenetic work (Mwanyambo tranthus in Flora Zambesiaca (Paton et al. 2013), the Namuli 2008, Paton et al. in prep) suggests that this broadly circum- plants could potentially key out to P. caudatus. However, when scribed Plectranthus is paraphyletic, with species formerly comparing the specimens side by side there were clear differ- placed in Coleus and Solenostemon forming a sister clade to ences immediately noticeable, such as a lack of the bright pink a large group of taxa including well-established and morpho- bracts within the inflorescences that are conspicuous in true logically distinct genera such as Aeollanthus Spreng., Alvesia P. caudatus specimens, smaller leaves which are not so mark- Welw., Capitanopsis S.Moore, Tetradenia Benth. and Thorn- edly bullate, and the inflorescences being more pyramidal in croftia N.E.Br., in addition to a large group of other species that shape and pedunculate rather than sessile. Closer examination have been placed in Plectranthus, including its type, P. fruti- under the microscope and measurement of floral characters cosus L’Hér. This molecular evidence is supported by recent revealed several other key differences to the specimens of morphological studies (Lukhoba et al. 2006, Paton et al. 2009, P. caudatus seen and to the available de scriptions of P. cau- 2013) that recognise the existence of a ‘Coleus’ clade within datus (Rendle et al. 1911, Paton et al. 2013). All relevant keys the broadly circumscribed Plectranthus based on the following to Plectranthus in Africa (Morton 1963, Codd 1975, Ryding diagnostic characters: – the posterior corolla lobe shorter than the anterior, and usu- 1 Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, United King- dom. ally markedly so with the anterior lobe often large and navi- 2 corresponding author e-mail: [email protected]. cular; © 2017 Naturalis Biodiversity Center You are free to share - to copy, distribute and transmit the work, under the following conditions: Attribution: You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). Non-commercial: You may not use this work for commercial purposes. No derivative works: You may not alter, transform, or build upon this work. For any reuse or distribution, you must make clear to others the license terms of this work, which can be found at http://creativecommons.org/licenses/by-nc-nd/3.0/legalcode. Any of the above conditions can be waived if you get permission from the copyright holder. Nothing in this license impairs or restricts the author’s moral rights. E. Downes & I. Darbyshire: Coleus namuliensis and Coleus caudatus from Mozambique and Zimbabwe 169 – the calyx usually asymmetric at the base with the pedicel attached behind the posterior lip; and shiny, with – the stamens free or fused. long; violet, or caducous or dots, mm The ‘Plectranthus’ clade, on the other hand, is characterised by fruit arrangement 30 flower, blue persistence in sessile having ± equal corolla lobes, a symmetrical calyx base with the in to reddish ‘1+4’ up pedicel attaching at the mid-line, and free stamens (Paton et long; long sometimes cm a long either with marked in al. 2009). A forthcoming paper making the case for the recogni- mm mm mm mm tion of Coleus at the generic rank and providing the necessary 3–5 White, to violet broadly elliptic, flattened, producing copious mucilage variable, 40–250 spikes more lax, rachis nearly always visible between verticils 2–4 1.5 2–3 Posterior lobe noticeably largest, lobes P. montanus P. new name combinations in Coleus is planned for publication in the near future (Paton et al. in prep). We therefore accept peduncle Coleus (including Solenostemon) as a distinct genus. We recognise that the species discussed in this paper are part of long; with Spikes and or this re-circumscribed genus, and so we name the new species mm speckles, Brown Coleus namuliensis E.Downes & I.Darbysh., and for any spe- 50 flower, fruit caducous lateral in to in sessile cies for which there is already a combination in Coleus we use 2013). darker up long; cm that name. We also make the new combination for the species long long either mm with mm between it is most likely to be confused with, Plectranthus caudatus (= arrangement mm mm (2009, Coleus caudatus (S.Moore) E.Downes & I.Darbysh.), as this al. mucilage 14–22 Blue flattened-ovoid, smooth, producing copious speckled ‘3+2’ 100–250 spikes more lax, rachis always visible between verticils 5–25 4–5 7–9 Posterior and lateral lobes larger, sinus giving a anterior lobes wider, P. lactiflorus P. updated name is needed for ongoing studies into the Chim- et animani endemics (see Discussion). We have refrained from making further new combinations here, pending the forthcoming Brown Paton peduncles paper on Coleus by Paton et al. (in prep.). lax, from short Spikes and speckles, part with more flower, fruit caducous Materials & METHODS lateral in or in in darker spikes long; long long cm The present study is based on the investigation of herbarium taken sessile mm with between mm arrangement mm mm specimens. The collections at the BM, K and SRGH herbaria are were consulted; abbreviations for herbaria follow the standard 10–16 ovoid, flattened, smooth, shiny, producing speckled mucilage 50–100 rachis visible between verticils 5–15 3–4 5–6 Posterior and lateral lobes larger, anterior lobes wider, giving a anterior lobes wider, P. crassus P. form listed on Index Herbariorum (Thiers, continuously updat- species peduncle; Blue Brown ed). All specimens cited have been seen except where noted Spikes with as ‘not seen’; those for which only images have been seen are dots, other purple ‘1+4’ sinus marked with an *. Prior to dissection, flowers were soaked in for or apart gland Aerosol OT 5 % solution; measurement of vegetative organs verticils narrower ‘3+2’ blue mm (weak) fruit noticeably were made on dry material. flower, 5 a caducous ± and in in to pale lobes reddish The assessment of the conservation status of the new species to mucilage up long; long cm giving long longer subsessile; with follows the categories and criteria of IUCN (2012).