Taxonomic reappraisal of the mangrove genus Avicennia (Acanthaceae) in India

A taxonomic reappraisal of the mangrove genus Avicennia in India was
undertaken through extensive field surveys and critical examination of
herbarium specimens. Three taxa, Avicennia alba, A. marina subsp. marina,
and A. officinalis, are described in detail. A synonymic list was compiled
using the World Checklist of Vascular Plants (WCVP) and assessed through
analysis of protologues and original material, with accompanying
nomenclatural notes. Accordingly, four lectotypes and one neotype were
designated. Leaf forms were investigated using principal component
analysis (PCA), as foliar characters have historically served as important
criteria for delimiting taxa within the genus. PCA was conducted under
four approaches: (1) among A. alba, A. marina, and A. officinalis; (2)
among four infraspecific taxa of A. marina; (3) across populations from
the three major coastal regions of India; and (4) between A. marina subsp.
marina and A. marina var. acutissima. In all cases, the analysis indicated
that leaf form alone could not reliably distinguish taxa. However,
PERMANOVA using quantitative variables employed in PCA showed that, in
first two cases, the differences among Avicennia species and among the
infraspecific taxa of A. marina were statistically significant. In
contrast, the differences among A. marina populations from the three major
coastal regions of India, as well as between A. marina subsp. marina and
A. marina var. acutissima, were weak. Phylogenetic analysis using ITS
sequences from India and other Indo–West Pacific Avicennia accessions
showed broad concordance with established multilocus frameworks; however,
several GenBank accessions displayed incongruent placements, suggesting
probable misidentifications. Similarly, inconsistency in GBIF occurrence
records further points to widespread identification errors. The findings
also indicate that A. officinalis populations from India are
morphologically distinct from conspecific populations in Australasia,
highlighting taxonomic complexity within the genus. To facilitate
identification, a taxonomic key to Avicennia taxa in India is provided.