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New molecular and morphological insights prompt transfer of Blechum to Ruellia (Acanthaceae)

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The genus Blechum P. Browne (Acanthaceae) is best known by the widespread tropical weed formerly referred to as Blechum pyramidatum (Lam.) Urb. (recently re-established as Ruellia blechum L.). Some species of Blechum have been transferred to Ruellia based on macromorphological and molecular data, but comprehensive study of taxa assigned to Blechum is lacking. We reexamined morphological characters that have been used to distinguish Blechum from Ruellia including inflorescence structure and pollen and capsule morphology. Second, we conducted phylogenetic analyses including nine accessions from five of six species traditionally treated in Blechum (and that we here consider valid species) plus a synoptic sample of species of Ruellia based on the work of the first author. Results indicate that Blechum is nested within Ruellia with strong support. An alternative phylogenetic hypothesis of monophyly of Ruellia exclusive of species traditionally treated in Blechum was rejected under a likelihood but not a parsimony criterion. Based on morphological similarities, common chromosome numbers, and molecular data, we transfer the genus Blechum to Ruellia. Third, we studied specimens and images of specimens of as many pertinent historical collections as we could acquire. This study resulted in nomenclatural and taxonomic renovations that include several new taxonomic synonyms (reduction of Blechum killipii, Blechum linnaei, and Blechum trinitense), two new combinations (Ruellia haughtii and Ruellia panamensis), one new lectotypification (Blechum brownei α subcordatum f. albiflorum), and additional recommendations for future typification. Based on our morphological and molecular studies, six species of Ruellia are treated as constituting the Blechum lineage of Ruellia. A preliminary key is provided to distinguish these species, but the Blechum lineage as a whole deserves further attention and fieldwork to determine the precise limits of each taxon.


Document Type: Research Article

Affiliations: 1: Duke University, Department of Biology, 137 Biological Sciences, Durham, North Carolina 27708, U.S.A., Rancho Santa Ana Botanic Garden, 1500 N. College Avenue, Claremont, California 91711, U.S.A.;, Email: 2: Department of Botany, California Academy of Sciences, 55 Music Concourse Drive, Golden Gate Park, San Francisco, California 94118, U.S.A. 3: The New York Botanical Garden, Institute of Systematic Botany, Bronx, New York 10458, U.S.A. 4: Rancho Santa Ana Botanic Garden, 1500 N. College Avenue, Claremont, California 91711, U.S.A.

Publication date: August 1, 2009


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