Polystachya siederi Hermans 2021, sp. nov.
Creators: name: Hermans, Johan
name: Rajaovelona, Landy
name: Cribb, Phillip
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Liliopsida
Asparagales
Orchidaceae
Polystachya
Polystachya siederi

description: <b>Polystachya siederi</b> <i>Hermans</i> <b>sp. nov.</b> Type: Madagascar, Mahajanga prov., Bealanana area, 924 m, Jan. 2017, <i>Sieder, Pertl, Prehsler &amp; Andriantiana</i> 7112 (leg. <i>Hermans</i> 8151), (holotype WU!). http://www.ipni.org/urn:lsid:ipni.org:names:77214549-1 A large erect creeping lithophytic <i>herb</i> up to 18 cm high, on a very short rhizome with the new growth emerging from the base or node of the old pseudobulbs, with a dense mass of thick glabrous greyish roots 2 – 3 mm in diam. <i>Pseudobulbs</i> conical to subcylindrical, 35 – 60 × 4 – 7 mm, longitudinally ridged, the older ones distinctly annulate at the old leaf joints, partly covered by several overlapping greyish-brown sheaths, 3 – 4 leaves towards the apex. <i>Leaves</i> linear-ligulate, attenuate at the tip, 8 – 15 × 1.2 – 1.5 cm, narrowed into a conduplicate petiole at the base, the basal one much smaller and almost bractlike, pale green. <i>Inflorescence</i> erect, surpassing the leaves, up to 18 cm, 1.2 – 2.1 mm in diam., densely racemose in the apical third with up to 9 flowers. <i>Peduncle</i> flattened – laterally compressed, almost glabrous towards the base but becoming echinatehirsute towards the rachis, generally with a prominent conduplicate leaf-like scale towards the middle (35 – 65 × 4 – 6 mm) and 2 – 4 thinner and much shorter amplectant sheaths. <i>Rachis</i> terete, not branched, 3 – 6 cm, flowering in succession, hirsute. <i>Floral bracts</i> lanceolate acuminate, persistent and thickened at the base, hirsute on the exterior especially towards the base, 3 – 3.2 × 1.5 – 2.1 mm. <i>Flowers</i> c. 10 × 9 mm, pure white except for the orange callus in the middle of the lip and farinose orange-yellow patch on the mid-lobe of the lip, the white ovary becoming green on fertilisation. <i>Pedicel</i> and <i>ovary</i> glabrous, fusiform, longitudinally ridged, 4.8 – 5.2 × 1.1 – 1.3 mm. <i>Dorsal sepal</i> ovate, acute, 5.1 – 5.5 × 3.4 – 3.7 mm, arching over the column. <i>Lateral sepals</i> spreading, forming an indistinct rounded mentum with the column foot, ovate, shortly acuminate, 5.4 – 5.6 × 5.4 – 5.9 mm. <i>Petals</i> oblanceolate, 4.2 – 4.3 × 1.9 – 2 mm, acute, incurved. <i>Lip</i> 5.1 – 5.3 × 4.9 – 4.8 mm, 3-lobed in the apical half, the lateral lobes porrect elliptic obtuse, the mid-lobe sub-triangular, ending in a short incurved apicule, margins rounded, the disc and mid-lobe minutely pubescent-farinose, disk with a distinct ovoid to almost globular callus in the centre, densely covered in farina. <i>Column</i> stout, 3-lobed, stigma rounded, transversally oblong, 2.5 – 3 × 1.5 – 1.6 mm; <i>anther</i> hemispherical with a rounded apical lobe, c. 1.1 × 1.2 mm; <i>pollinia</i> (2) ovoid, c. 0.8 × 0.6 mm. <i>Seed capsule</i> fusiform, c. 15 × 5 mm. Figs 9, 10. <b>RECOGNITION</b>. <i>Polystachya siederi</i> is distinct in having ascending pseudobulbs on a very short rhizome, large leaf-like scales towards the middle of the inflorescence, an unbranched inflorescence densely racemose towards the apex, hirsute rachis and floral bracts, medium-sized flowers with ovate lateral sepals forming a short rounded mentum at the base, a lip three-lobed in the apical half, and a farinose disk with an ovoid to globular callus in the centre. Amongst the <i>Polystachya</i> Hook. (Hooker 1824: t.103) species occurring in Madagascar, <i>P. siederi</i> has some vegetative and floral similarities to <i>P. anceps</i> Ridl. (Ridley 1885: 473), <i>P. heckeliana</i> Schltr. (Schlechter 1913: 167) and <i>P. rhodochila</i> Schltr. (Schlechter 1916: 323) but it differs in having an unbranched inflorescence, slightly smaller flowers, and more oval lateral sepals and lip shape; it also has much shorter floral bracts than <i>P. rhodochila</i>. In flower shape it is most similar to <i>P. heckeliana</i> but the lip is lobed in the apical half (vs the basal half), the callus is more distinct and the flower colour is also different. It shares a number of characteristics with several <i>Polystachya</i> from mainland Africa: the inflorescence, lip shape and callus are most similar to <i>P. transvaalensis</i> Schltr. (Schlechter 1895: 28) and <i>P. albescens</i> Ridl. (Ridley 1887: 199) and its variants but it is distinct from both by its shorter and broader pseudobulbs, unbranched inflorescence, and slightly smaller flowers with shorter and more rounded ovate lateral sepals. <b>DISTRIBUTION</b>. Endemic to Mahajanga province in northern Madagascar, only known from the type collection. <b>HABITAT</b>. In semi-shade in riverine forest on rock. Elevation 900 m. <b>CONSERVATION STATUS</b>. <i>Polystachya siederi</i> is known from one location, outside a protected area in Sofia region, Mahajanga province. The habitat, the extent of occurrence and the area of occupancy face continuing decline due to fire and agricultural practices. <i>Polystachya siederi</i> is therefore assessed as Critically Endangered CR B1ab(i,ii,iii) + 2ab(i,ii,iii). <b>FLOWERING TIME</b>. January. <b>ETYMOLOGY</b>. Named for Anton Sieder of the Botanical Garden, University of Vienna, Austria; an intrepid explorer, grower and connoisseur of the orchids of Madagascar. <b>NOTES</b>. <i>Polystachya</i> is a pantropical genus of about 250 epiphytic, lithophytic or terrestrial plants, with the greatest diversity in sub-Saharan tropical Africa (Cribb in Pridgeon <i>et al.</i> 2014: 455). There are currently 23 <i>Polystachya</i> species recognised from the Madagascar, Mascarene and Comoro region, 16 of which are only found on Madagascar and three have a wider distribution outside the region.
description: Published as part of <i>Hermans, Johan, Rajaovelona, Landy &amp; Cribb, Phillip, 2021, New species in Orchidaceae from Madagascar, pp. 39-56 in Kew Bulletin 76</i> on pages 49-54, DOI: 10.1007/S12225-021-09923-W, http://zenodo.org/record/5828128
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