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Paracostus C. Specht

Type: Paracostus englerianus (K. Schum) C. Specht

Description:
     Prostrate rhizomatous herbs or ascending as a climbing herb, 10-50cm in height with one or a few leaves each of which potentially subtends an axillary inflorescence. Rhizomes long, creeping. Leaves 1-4 per stem, fleshy, attached to sheath by short petiole. Vegetation entirely glabrous. Ligule short. Inflorescence an abbreviated spike emerging directly from the axis of a solitary leaf, few-flowered. Bracts membranaceous, green, unappendaged. Bracteole chartaceous, tubular. Calyx 3-lobed, lobes of equal size. Corolla tube exserted from the calyx; lobes membranous, narrow, lanceolate. Labellum large, obovate, thin, forming a long narrow tube that opens broadly to ovate at the apex, greatly exceeding petals and bracts in length, never lobed; white, sometimes with a yellow spot at the center directly opposite the fertile stamen. Stamen petaloid; tip reflexed, triangular, covering the opening of the floral tube. Ovary trilocular. Stigma cup-shaped without appendage. Fruit globose, capsular. Seeds angled with a membranaceous aril.

Geographical Distribution:
     Africa (Paracostus englerianus) and South East Asia (Paracostus paradoxus).

Phylogeny and Classification:
     Paracostus was first defined by Schumann (1899) as one of his five subgenera of Costus. Subsequent local floras rarely included mention of this subgenus as the only two species included do not occur in the same local floristic region. Maas (1979) recognizes the subgenus in his description of Costus paradoxus as part of his treatment of Asiatic and Australian Costaceae, mentioning the affiliation between this taxon and Costus englerianus of Africa.
     
     The two species placed in the subgenus Paracostus by Schumann are found to be sister taxa in recent phylogenetic analyses using molecular and morphological data, and furthermore are not included within any other major clade within the Costaceae. Together, the two Paracostus taxa are found to be sister to the Cheilocostus plus Tapeinochilos lineage of South East Asia. Thus the morphological and habit-based similarities of these two taxa as noted by Schumann in his description of subgenus Paracostus are upheld.

Taxonomic Diversity:
     Two species are placed in this genus: Paracostus englerianus and Paracostus paradoxus.

Paracostus paradoxus from Borneo.
Paracostus englerianus photographed at Lyon Arboretum.

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