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Pollen Morphology of Kalmia L. (phyllodoceae, Ericaceae) and Its Taxonomic Significance

A.K.M. Golam Sarwar
Laboratory of Systematic Botany, Graduate School of Agriculture, Hokkaido University, Japan

Hideki Takahashi
Laboratory of Systematic Botany, Graduate School of Agriculture, Hokkaido University, Japan

Abstract/ Executive Summary:

Pollen morphology of seven taxa of Kalmia was examined using light and scanning electron microscopy (LM and SEM, respectively), or SEM alone, in search of new characters that might contribute to infrageneric classification of the genus. The Kalmia species are stenopalynous and characterized by 3-colpor(oid)ate, medium, oblate pollen united in tetrahedral tetrads with rugulate exine sculpture. However, a continuous and serial variation in all the quantitative characters and exine sculpture was revealed within the genus. Kalmia buxifolia is characterized by having the smallest pollen tetrads, largest aperture, largest 2f/D ratio and septum thicker than apocolpial exine. On the other hand, K. latifolia produces the largest pollen tetrads with smallest aperture and smallest 2f/D ratio. An evolutionary trend from rugulate to psilate has also been observed in apocolpial exine sculpture of the genus Kalmia. On the basis of acetolysed pollen characteristics, a dichotomous key for Kalmia was prepared.

Keywords: Pollen morphology; Infrageneric classification; Exine sculpture; Kalmia.

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Program Area: Conservation and Biodiversity

Commodity: Plant

Objectives:

We present here a general pollen survey on Kalmia based on LM and SEM to search new character that could add information pertinent to infrageneric classification of this genus.

Methodology:

Pollen morphology of seven taxa (and 11 specimens) out of 11 species of Kalmia was examined by means of LM and SEM, or SEM alone. The remaining four species were not examined due to unavailability of herbarium specimens (and/or pollen samples) in the herbaria consulted here as well as others (Sarwar, 2011; for the complete list of herbaria consulted). Polliniferous materials used in this investigation were taken from the dried specimens from the herbaria S, SAPS and SAPT. Abbreviation of the herbarium names except for SAPT (the Botanic Garden, Hokkaido University, Sapporo) are according to the Index Herbariorum (Holmgren et al., 1990). Pollen grains were acetolysed following the technique of Erdtman (1960) modified by Takahashi (1987). Palynological features of three Kalmia species were studied both acetolysed and non-acetolysed condition to find out the effect of acetolysis on its pollen. For LM, the dehydrated (in an ethanol series) pollen (both acetolysed and non-acetolysed) was mounted in silicone oil (viscosity 3000 cs), and examined and measured with a Nikon Eclipse E200 microscope. The dimensions “D”, “P”, “d (E)” and “2f”, corresponding to the tetrad diameter, polar length, equatorial length and colpus length of pollen grain were measured, and the D/d, P/E and 2f/D ratio was calculated (Oldfield, 1959). The arithmetic mean, standard deviation and the maximum and minimum values were calculated using the XLSTAT 2009.3 program. Principal component analysis (PCA) and agglomerative hierarchical clustering (AHC) were also conducted using the same program to visualise the relationships among the studied species based on pollen data. A dendrogram was built by AHC. Pollen slides of all collections are deposited at the Hokkaido University Museum, Sapporo, Japan. Pollen size and shape classes were made following Erdtman (1986) and descriptive terminology follows Punt et al. (2007) and Sarwar et al. (2006). For SEM, the pollen samples, both acetolysed and non-acetolysed, were dehydrated in an ethanol series, and mounted and air dried on aluminum stubs from 70% ethanol, and sputter coated with Platinum-Palladium by a Hitachi E102 ion sputter. Subsequently, these were examined and photographed with a Jeol JSM-5310 LV scanning electron microscope operated at 15 KV. The SEM micrographs of apocolpial exine sculpture of similar position were used for the purpose of description and comparison.

Source of Information: Bangladesh J. Plant Taxon. 19(2): 123-133, 2012 (December)

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Achievement/Findings:

Inclusion of the two monotypic genera, Leiophyllum and Loiseleuria in Kalmia and, in consequence, the resurrection of K. buxifolia and K. procumbens, respectively has recently been proposed (Kron et al., 2002). Pollen morphological features, in general, showed similarities and may support the inclusion of these two taxa in Kalmia, but also showed some distinct variations viz. thicker septum compared to apocolpial exine, exine sculpture tending to psilate, etc. Pollen tetrads of K. buxifolia showed the characteristic rugulate apocolpial exine sculpture of Kalmia, however, it possesses some exceptional pollen characters within Kalmia, viz. smallest tetrads, largest aperture, largest 2f/D ratio and septum thicker than apocolpial exine. In the AHC analysis, K. buxifolia is the only member of Cluster 2, which was sister to Cluster 3.

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