Polystachya siederi Hermans 2021
Photo by © Anton Sieder/TYPE Drawing by Judi Stone and Kew Bull. 76: 40 J Hermans 2021
EARLY 
Common Name Sieder's Polystachya [Anton Sieder of the Botanical Garden, University of Vienna, Austria; an intrepid explorer, grower and connoisseur of the orchids of Madagascar current]
Flower Size .4" [1 cm]
Found in Mahajanga province of Madagascar in semi-shade in riverine forest on rock at elevations around 900 to 950 meters as a small sized, warm growing lithophyte with a very short rhizome with a dense mass of thick glabrous greyish roots and giving rise to a growth emerging from the base or node of the old conical to subcylindrical, longitudinally ridged, the older ones distinctly annulate at the old leaf joints, pseudobulbs partly enveloped by several overlapping greyish-brown sheaths, and carrying 3 to 4 towards the apex, linear-ligulate, attenuate at the tip, narrowing below into a conduplicate petiole at the base, the basal one much smaller and almost bract-like, pale green leaves that blooms in the early summer on an erect, surpassing the leaves, up to 7.2" [18 cm] long, Peduncle flattened, laterally compressed, almost glabrous towards the base but becoming echinate-hirsute towards the rachis, generally provided with a prominent conduplicate leaf-like scale towards the middle and 2 to 4 thinner and much shorter amplectant sheaths, the rachis terete, not branched, 1.2 to 2.4" [3 6 cm], hirsute, densely racemose in the apical third with successively 1 to few up to 9 flowered inflorescence with lanceolate acuminate, persistent and thickened at the base, hirsute on the exterior especially towards the base, shorter than the ovary floral bracts and carrying pure white flowers except for the orange callus in the middle of the lip and farinose orange-yellow patch on the mid-lobe of the lip.
"Polystachya siederi 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 Polystachya species occurring in Madagascar, P. siederi has some vegetative and floral similarities to P. anceps, P. heckeliana and P. rhodochila 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 P. rhodochila. In flower shape it is most similar to P. heckeliana 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 Polystachya from mainland Africa: the inflorescence, lip shape and callus are most similar to P. transvaalensis and P. albescens 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." Hermans 2021
Synonyms
References W3 Tropicos, Kew Monocot list , IPNI ;
* Kew Bull. 76: 40 J Hermans 2021 Photo/drawing fide
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