THAI FOR. BULL. (BOT.) 43: 4–14. 2015. Pollen morphology of Combretaceae from Thailand and its taxonomic signifi cance PUNTIWA KRACHAI1,2 & PIMWADEE PORNPONGRUNGRUENG1,* ABSTRACT. The pollen morphology of 30 taxa from six genera of Thai Combretaceae, including one species each of Anogeissus and Calycopteris, two species each of Lumnitzera and Quisqualis, 11 species of Combretum and 13 species of Terminalia (including one introduced species), was investigated to determine its taxonomic signifi cance. The pollen samples were acetolyzed and investigated under light and scanning electron microscopy. Pollen morphology of Thai Combretaceae was described, compared and discussed along with its taxonomic implications. The taxonomic signifi cance of pollen morphological characters for Thai Combretaceae is limited. The pollen grains were found to be monads, radially symmetrical, isopolar, small- to medium-sized, heterocolpate (tricolporate alternating with subsidiary colpi). The taxa studied can be divided into two groups and nine subgroups according to the fusion of subsidiary colpi at the polar area and the exine sculpturing patterns. However, this grouping is not congruent with the taxonomic classifi cation of the family based on morphological as well as molecular data. KEY WORDS: Combretaceae, Pollen, Taxonomy, Thailand. INTRODUCTION Thailand were classifi ed into two tribes and three subtribes, including the tribe Laguncularieae con- The family Combretaceae belongs to the order taining the single genus Lumnitzera Willd.; the Myrtales, and comprises ca 20 genera and 500 species tribe Combreteae with two subtribes: Combretinae (Heywood et al., 2007; APG III, 2009). The family containing three genera: Calycopteris Lam. ex Poir., is distributed throughout the tropics, with some Combretum L oefl . a n d Quisqualis L . , and Terminaliinae extensions to subtropical and warm-temperate containing two genera: Anogeissus (DC.) Wall. ex regions (Exell & Stace, 1966; Heywood et al., Guillem. & Perr. and Terminalia L. (classifi cation 2007; Stace, 2007). The family is divided into two follows Stace, 1966). subfamilies, Strephonematoideae and Combretoideae. The fi rst one contains the single genus Strephonema Studies of pollen morphology of Combretaceae Hook.f., and the latter contains most of the genera. were carried out by a number of previous authors. The subfamily Combretoideae was previously divided Erdtman (1966) stated that pollen grains of into four tribes: Calycopter-ideae, Combreteae, Combretaceae are tricolporate or tricolporate with Laguncularieae and Terminalieae (Exell, 1954). pseudocolpi, prolate to prolate-spheroidal in shape, More recently, the subfamily was divided into only with the sexine evidently thinner than the nexine. two tribes, Laguncularieae and Combreteae, and The pollen grains of this family are similar to those the latter tribe was subdivided into three subtribes: of Melastomataceae but differ from Myrtaceae, Combretinae, Pteleopsidinae and Terminaliinae (Exell Punicaceae and Sonneratiaceae, which are all clas- & Stace, 1966; Stace, 2007). Only the subfamily sifi ed in the same order Myrtales according to APG Combretoideae is present in Thailand, with seven III (2009). A more detailed study was produced by genera and 47 species (Nanakorn, 1985, 1986; Pooma Patelet al. (1984), who recognized the Combretaceae & Suddee, 2014). The member of Combretaceae in pollen to be isopolar, radially symmetrical, 1 Applied Taxonomic Research Center, Department of Biology, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand 2 present address: Program of Biology, Department of Science, Faculty of Science and Technology, Loei Rajabhat University, Loei 42000, Thailand *Correspondent author: [email protected] SW 8736-p004-014-G8.indd 4 12/1/58 BE 8:59 PM POLLEN MORPHOLOGY OF COMBRETACEAE FROM THAILAND AND ITS TAXONOMIC SIGNIFICANCE 5 (P. KRACHAI & P. PORNPONGRUNGRUENG) tricolporate (rarely tetracolporate), or heterocol- kept at Queen Sirikit Botanic Garden Herbarium pate with three colporate alternating with three (QBG). The list of voucher specimens included in subsidiary colpi, and subsidiary colpi united or this study is given in Appendix 1. The pollen grains separated at the polar area, spheroidal to subprolate were acetolyzed following the methods described shape in equatorial view, circular or hexagonal by Erdtman (1966). For light microscopy, the ace- outline in polar view, with the exine sculpturing tolyzed pollens were mounted in silicone oil and GLYHUVH IURP VWULDWH SVLODWH ¿QHO\ UXJXODWH WR sealed with paraplast. Permanent slides are kept at rugulate. These authors also suggested that the Khon Kaen University Herbarium (KKU). At least &RPEUHWDFHDHSROOHQFDQEHGLYLGHGLQWR¿YHSROOHQ 15 pollen grains per taxa were used to measure the groups based on the presence of subsidiary colpi polar axis (P), equatorial axis (E), exine thickness and exine sculpturing. El Ghazali et al. (1998) in polar view (EX) and colpus length (CL). For investigated 18 genera and 130 species of scanning electron microscopy, acetolyzed pollen Combretaceae and reported that the pollen are grains were suspended in a drop of absolute alcohol, monads, isopolar, radially symmetrical, tricolporate then transferred to aluminum stubs, air-dried and or heterocolpate. Nine pollen types and two subtypes coated with gold-palladium. SEM micrographs were were recognized based on pollen class, aperture taken with a Leo 1450VP SEM. The terminology types, thickening of the exine around the endoaper- and pollen size classes follow Walker & Doyle tures, costae endopori, pollen size, exine sculpturing (1975) and Punt et al. (2007). and shape in polar view. They reported that pollen morphological data do not support the current RESULTS taxonomic treatment of the family. Stace (2007) reported two pollen types: tricolporate and hetero- The description of pollen morphological FROSDWHWKH¿UVWW\SHIRXQGLQBuchenavia Eichler, characters is provided in alphabetical sequence by Laguncularia C.F.Gaertn. and Strephonema, while tribe, subtribe and genera, while the characters of the latter type is found in the other genera including the taxa are summarized in Table 1. Anogeissus, Calycopteris, Combretum, Conocarpus Tribe Combreteae: subtribe Combretinae L., Guiera Adans. ex Juss., Lumnitzera, Macrop- teranthes F.Muell ex Benth., Pteleopsis Engl. and Calycopteris (Fig. 2D–F): Terminalia. He pointed out that the exine sculpturing Monads, radially symmetrical, isopolar, P = varies between species in the group with tricolporate 18–23 μm, E = 18–23 μm, small, prolate-spheroidal, grains but quite similar in the group with hetero- heterocolpate, colpus length 13–18 μm, subsidiary colpate grains. Moreover, the pollen morphology colpi separated at the polar area, exine thickness cannot be used for clarifying the relationship 1–2 μm, perforate-microrugulate between genera. However, these characters might KHOS LQ LGHQWL¿FDWLRQ RI VRPH WD[D 7KH SROOHQ Combretum (Figs. 1A–C, 2G–I): morphology of the family has never been studied in Thailand. The aims of the present work were Monads, radially symmetrical, isopolar, P = to classify, describe, and illustrate the pollen char- 14–30 μm, E = 14–29 μm, small to medium, spherical, acteristics of Thai Combretaceae and to assess the prolate-spheroidal, subprolate, oblate-spheroidal, taxonomic value of these characters. heterocolpate, colpus length 11–27 μm, subsidiary colpi fused or separated at the polar area, exine thickness 1–2 μm, perforate-microrugulate, striate MATERIAL AND METHODS or microrugulate. The pollen of 30 taxa of Combretaceae in Quisqualis (Figs. 1D–F, 2J–L): Thailand (including one introduced species, Terminaia ivorensis A.Chev.) was examined using Monads, radially symmetrical, isopolar, P = light microscopy (LM) and scanning electron 28–40 μm, E = 29–42 μm, medium, oblate-spheroidal microscopy (SEM). Pollen samples were collected or prolate-spheroidal, heterocolpate, colpus length IURP WKH ¿HOG FROOHFWLRQV DURXQG 7KDLODQG DQG 24–33 μm, subsidiary colpi fused or separated at the some taxa were taken from herbarium specimens polar area, exine thickness 2–3 μm, microrugulate or reticulate. SW 8736-p004-014-G8.indd 5 12/7/58 BE 1:59 PM 6 THAI FOREST BULLETIN (BOTANY) 43 Tribe Combreteae: subtribe Terminaliinae subtribe Terminaliinae have only a small sized-grains whereas subtribe Combretinae and Laguncularieae Anogeissus (Fig. 2A–C): have a small to medium sized-grains. The largest Monads, radially symmetrical, isopolar, P = size was found in Q. indica (P = 37–40 μm, E = 38– 12–14 μm, E = 11–14 μm, small, prolate-spheroidal, 42 μm) and the smallest was found in A. acuminata heterocolpate, colpus length 9–11 μm, subsidiary (P = 12–14 μm, E = 11–14 μm). The pollen shape in colpi separated at the polar area, exine thickness equatorial view varied among species. Most species 1–1.5 μm, microechinate. are prolate-spheroidal in pollen shape and a few species are oblate-spheroidal, subprolate and spherical. Terminalia (Figs. 1G–L, 3G–L): The amb outline is circular or hexagonal. Monads, radially symmetrical, isopolar, P = Even though the pollen morphological char- 13–21 μm, E = 12–19 μm, small, prolate-spheroidal DFWHUVDUHLQVXI¿FLHQWWRLGHQWLI\DOOVSHFLHVVWXGLHG or subprolate, heterocolpate, colpus length 9–18 μm, the exine sculpturing is possibly a helpful character subsidiary colpi fused or separated at the polar area, for distinguishing some species because it varies exine thickness 1–2 μm, perforate-microrugulate DPRQJ VSHFLHV DQG VRPH VSHFLHV