Botanical Journal of the Linnean Society, 2009, 159, 155–162. With 28 figures Palynological survey of subtribe Pithecocteniinae (Bignonieae, Bignoniaceae) CARLOS M. BURELO-RAMOS1*, FRANCISCO G. LOREA-HERNÁNDEZ2 and ANDREW P. VOVIDES3 1 Posgrado en Sistemática, Instituto de Ecología, A.C., Km. 2.5 Antigua Carretera a Coatepec no. 351, Apartado Postal 63, Xalapa 91070, Veracruz, Mexico 2 Herbario XAL, Instituto de Ecología, A.C., Km. 2.5 Antigua Carretera a Coatepec no. 351, Apartado Postal 63, Xalapa 91070, Veracruz, Mexico 3 Laboratorio de Biología Evolutiva de Cycadales, Departamento de Biología Evolutiva, Instituto Ecología, A.C., Km. 2.5 Antigua Carretera a Coatepec no. 351, Apartado Postal 63, Xalapa 91070, Veracruz, Mexico Received 24 January 2007; accepted for publication 5 June 2008 The pollen morphology of subtribe Pithecocteniinae was reviewed. Thirty species of the six genera currently recognized, namely Amphilophium, Distictis, Distictella, Glaziovia, Haplolophium and Pithecoctenium, were considered. All the species surveyed fell into one of the two pollen groups: (1) inaperturate, spheroid pollen; and (2) stephanocolpate, prolate pollen. The former group included the studied species of Distictis, Distictella and Pithecoctenium, the latter species of Amphilophium, Glaziovia and Haplolophium. The variation of exine sculpture and thickness did not show any taxonomic relationships. An argument for considering pollen features, together with other morphological characters, to elucidate monophyletic units within Pithecocteniinae is presented. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159, 155–162. ADDITIONAL KEYWORDS: Amphilophium – Distictis – Distictella – Glaziovia – Haplolophium – palynology – Pithecoctenium – pollen morphology. INTRODUCTION Pollen morphology has been found to be highly conservative within the genera of Bignoniaceae and, as a result, is of high taxonomic value at the generic level in this family (Gentry & Tomb, 1979; Bove, 1993, 1994). In terms of pollen morphology, Bignonieae is the most diverse tribe in Bignoniaceae, presenting seven pollen types among its genera. Tricolpate pollen is widely represented within the genera of this tribe, being found in 22 of the 45 genera (Buurman, 1977; Gentry & Tomb, 1979). Current knowledge of the pollen features in subtribe Pithecocteniinae Melch. comes from ten species studied in investigations of different palynological scope (Schumann, 1895; Urban, 1916; Suryakanta, *Corresponding author. E-mail: francisco.lorea@inecol.edu.mx 1973; Gentry & Tomb, 1979; Silvestre & Melhem, 1989; Bove, 1993, 1994): Amphilophium paniculatum H.B. & K., Distictella magnoliifolia (Kunth) Sandwith, Distictis buccinatoria (DC.) A.H.Gentry, D. granulosa Bureau & K.Schum, Haplolophium bracteatum Cham., H. dusenianum Kraenzl., Glaziovia bauhinioides Bureau ex Baill., Pithecoctenium crucigerum (L.) A.H.Gentry, P. dolichoides (Cham.) Bureau ex K.Schum. and P. hatschbachii A.H.Gentry. In this work, we consider Pithecocteniinae to be comprised of the genera Amphilophium, Distictis, Distictella, Glaziovia, Haplolophium and Pithecoctenium, in contrast to the concept of the subtribe established by Melchior (1927). Our circumscription is based on the revision by Gentry (1973, 1974, 1976, 1993: 264–282), and the recent phylogenetic analysis of Bignoniacecae by Lohmann (2006). According to Gentry’s series of floristic studies, the subtribe is composed of 43 species. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159, 155–162 155 156 C. M. BURELO-RAMOS ET AL. Table 1. List of species and specimens studied Species Specimens Amphilophium aschersonii Ule A. blanchetii (DC.) Bureau & K. Schum. A. ecuadorense A.H.Gentry A. paniculatum (L.) Kunth A. paniculatum var. imatacense A.H.Gentry A. paniculatum var. molle (Schltdl. & Cham.) Standl. A. perbracteatum A.H.Gentry A. sandwithii Fabris Distictella cuneifolia (DC.) Sandwith Da. dasytricha Sandwith Da. elongata (Vahl) Urb. Da. laevis (Sandwith) A.H.Gentry Da. magnoliifolia (Kunth) Sandwith Da. mansoana (DC.) Urb. Da. monophylla Sandwith Da. obovata Sandwith Da. parkeri (DC.) Sprague & Sandwith Da. reticulata A.H.Gentry Distictis buccinatoria (DC.) A.H.Gentry D. granulosa Bureau & K.Schum. D. lactiflora (Vahl) DC. D. laxiflora (DC.) Greenm. D. pulverulenta (Sandwith) A.H.Gentry D. staminea (Lam.) A.H.Gentry Glaziovia bauhinioides Bureau ex Baill. Haplolophium bracteatum Cham. H. glaziovii (Bureau ex K. Schum.) A.H.Gentry H. rodriguesii A.H.Gentry Pithecoctenium crucigerum (L.) A.H.Gentry P. cynanchoides DC. P. dolichoides (Cham.) Bureau ex K.Schum. P. hatschbachii A.H.Gentry Revilla 2045 (NY); Rimachi 967 (F) Harley 21286 (SP); Harley et al. 18904 (NY) Díaz & Vázquez 2731 (NY); Boecke 2293 (NY) García 151 (XAL); Castillo & Pedraza 2141 (XAL) Lindeman et al. 11 (NY); Giulietti et al. 133 (HUEFS) Calzada et al. 6169 (XAL); Castillo & Golberg 2924 (XAL) Silva et al. 426 (HUEFS); Guedes 51578 (HUEFS) Nee & Vargas 43424 (NY); Nee et al. 37394 (NY) Cid et al. 497 (NY); Amaral et al. 112323 (NY) Maciel 4603 (NY) Leg 3095 (NY); Irwin et al. 12021 (NY) Zarucchi et al. 2600 (NY); Anderson 10783 (NY) Revilla 1790 (MEXU); Gentry 12969 (XAL) Montovani 1432 (XAL); Montovani 1376 (SP) Maguire et al. 41805 (NY); Hubber & Medina 5892 (NY) Maguire et al. 43837 (NY); Steyermark 9380 (NY) Cowan & Sanderson 2168 (NY); Gleason 755 (NY) Coelho & Nello 3940 (SP) Burelo 138 (XAL); Miranda & Macias 2107 (MEXU) Anderson et al. 35669 (RB); Lindeman 222 (NY) Britton & Cowell 1268 (NY); Zanoni et al. 34952 (NY) Shilom 2140 (NY); Zolá et al. 355 (XAL) Vicentini 1074 et al. (RB); Hopkins et al. 1551 (SPF) Leonard & Leonard 12329 (NY); Alain & Liogier 22640 (NY) Herringer 2096 (SP); Kuhlmann s/n (SP) Nadruz et al. 521 (NY); Brade 7045 (SP) Ritz & Klein 18126 (NY); Hatschbach et al. 66533 (SPF). Sperling 5857 (NY); Sperling 5931 (NY) Burelo 137 (UJAT); Luna & Zolá 304 (XAL). Galleto 1024 (XAL); Pensiero & Morino 4288 (NY) Gonçalves s/n (XAL); Silva 24 (HUEFS) Bernacci 25906 (UEC); Hatschbach 18505 (MBM) We describe the pollen morphology in Pithecocteniinae in order to provide additional information that can be used for taxonomic evaluation. Finally, we discuss the possible taxonomic implications of the morphological features found in the pollen of this group of species. MATERIAL AND METHODS Pollen of 30 species and three varieties of Pithecocteniinae was studied (Table 1): six of the eight species of Amphilophium, ten of the 14 species of Distictella, six of the 12 species of Distictis, the only species of Glaziovia, three of the four species of Haplolophium and the four species of Pithecoctenium. In material borrowed from herbaria, there were no specimens with suitable flowers to obtain pollen for the remaining species. Two samples per herbarium specimen were taken, one for light microscopy and one for observation by scanning electron microscopy (SEM). All pollen samples were subjected to standard acetolysis (Erdtman, 1952), except for the pollen of Pithecoctenium species, which was treated twice, as, after the first acetolysis, pollen grains were not sufficiently clear for analysis by light microscopy. Processing for light microscopy included the immersion of acetolysed grains in a 2 : 1 glycerin and water mix, and further mounting under a glass coverslip sealed with glycerine jelly. From these samples, measurements of polar (PL) and equatorial (EL) dimensions, as well as ektexine (EK) and endexine (EN) thickness, were obtained. At least 25 pollen grains were measured for each species. A survey of the type and number of apertures, as well as exine ornamentation, was also based on these samples. Samples of acetolysed grains for analysis by SEM were dehydrated through immersion in progressively higher concentrations of alcohol solutions. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159, 155–162 PALYNOLOGY OF THE SUBTRIBE PITHECOCTENIINAE 157 Table 2. Pollen types in Pithecocteniinae Inaperturate pollen, macro-reticulate Inaperturate pollen micro-reticulate Stephanocolpate pollen, macro-reticulate Stephanocolpate pollen, micro-reticulate Distictella cuneifolia Da. Dasytricha Da. elongata Da. magnoliifolia Da. mansoana Da. monophylla Da. Obovata Da. reticulata Distictis laxiflora D. pulverulenta D. staminea Pithecoctenium crucigerum P. cynanchoides P. dolichoides Distictella laevis Da. parkeri Glaziovia bauhinioides Distictis buccinatoria D. granulosa D. lactiflora P. hatschbachii Haplolophium glaziovii Amphilophium aschersonii A. blanchetti A. ecuadorense, A. paniculatum A. paniculatum var. molle A. paniculatum var. imatacense A. perbracteanum A. sandwithii H. rodriguesii H. bracteatum H. nunezii From these samples, high-resolution details of apertures and exine ornamentation were obtained. The description of the pollen grain surface is based on the work of Bove (1994), in which the ornamentation composed of a reticulum in which the unit cells correspond to 10% or more of the longest axis is called macro-reticulate, and a surface with unit cells of the reticulum up to 2% of that axis is considered to be micro-reticulate. The rest of the terms used here for pollen descriptions were taken from Halbritter et al. (2005) and the studies of Bignoniaceae by Gentry & Tomb (1979) and Bove (1993, 1994). RESULTS Two basic pollen types were distinguished in the studied species: (1) spheroid, inaperturate grains; and (2) prolate, 7–10-aperturate (stephanocolpate) grains. Taking into account the size of the reticulum, both types can be divided again into two groups each, namely micro-reticulate and macro-reticulate (Table 2). Inaperturate pollen is present in all species of Distictella, Distictis and Pithecoctenium surveyed (Figs 1–8). A macro-reticulate pollen surface in this group is found in Distictella cuneifolia, Da. dasytricha, Da. elongata, Da. magnoliifolia, Da. mansoana, Da. monophylla, Da. obovata, Da. reticulata, Distictis laxiflora, D. pulverulenta, D. staminea, Pithecoctenium crucigerum, P. cynanchoides and P. dolichoides. A micro-reticulate surface is present in Da. laevis, Da. parkeri, D. buccinatoria, D. granulosa, D. lactiflora and P. hatschbachii. Pollen grains in all the species mentioned above are radially symmetric, apolar, spheroid, with granules within the lumina of the reticulum, semitectate and with simple-baculate waved muri. Morphometric features show a wide variation among species (Table 3; Fig. 9); the smallest sized pollen grains are found in D. staminea (45.1 mm), with a greater diameter found in Da. cuneifolia and Da. reticulata at 71.4 mm and 70.3 mm, respectively. The thicknesses of the columns and tectum are, in most species, less than 1 mm, but, in Da. magnoliifolia and Da. parkeri, these structures can reach 2 mm, and, in Da. cuneifolia, they can even be 3–4 mm thick. Stephanocolpate pollen is shown by all species of Amphilophium (Figs 10–18), Glaziovia and Haplolophium (Figs 19–27). A macro-reticulate pollen surface is found in Glaziovia bauhinioides and Haplolophium glaziovii. However, a micro-reticulate surface is present in Amphilophium aschersonii, A. blanchetii, A. ecuadorense, the three varieties of A. paniculatum, A. perbracteatum, A. sandwithii, Haplolophium bracteatum and H. rodriguesii. Pollen in the group of species mentioned above is radially symmetric, prolate, seven- to ten-colpate, with granules within the lumina, and simple-baculate waved muri. Considering the average measurements of the pollen in these species (Table 4; Figs 9, 28), H. glaziovii had the largest pollen grains (82.4 ¥ 81 mm) and H. rodriguesii the smallest grains (49.58 ¥ 71.9 mm). Half of the studied species had columns and tectum up to 2 mm thick (A. paniculatum, A. perbracteatum, G. bauhinioides, H. glaziovii and H. rodriguesii), and up to 1 mm thick in the other half of the species. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159, 155–162 158 C. M. BURELO-RAMOS ET AL. Figures 1–8. Exine sculpturing of inaperturate pollen in Pithecocteniinae. Figs 1, 2. Distictis lactiflora. Fig. 1. ¥1900; scale bar, 10 mm. Fig. 2. ¥3500; scale bar, 2 mm. Figs 3, 4. Distictella elongata. Fig. 3. ¥1300; scale bar, 10 mm. Fig. 4. ¥5000; scale bar, 5 mm. Figs 5, 6. Distictella parkerii. Fig. 5. ¥1300; scale bar, 10 mm. Fig. 6, ¥4000; scale bar, 5 mm. Figs 7, 8. Pithecoctenium hatschbachii. Fig. 7. ¥1500; scale bar, 10 mm. Fig. 8. ¥4000; scale bar, 5 mm. POLLEN AND SYSTEMATICS OF PITHECOCTENIINAE THE As stated by Gentry & Tomb (1979), pollen features can be assessed in a taxonomic context as one of several indicators of evolutionary relationships. Based on our findings, in terms of pollen morphology, we can recognize two main groups within the Pithecocteniinae: one with inaperturate, spheroid pollen, and the other with stephanocolpate, prolate pollen. As far as the sample surveyed showed, these did not interchange, i.e. all species of any genus analysed had one or other of these two pollen conditions. Using the current best phylogenetic hypothesis for Bignonieae (Lohmann, 2006) to trace pollen types, it is clear that both inaperturate and stephanocolpate types found in Pithecocteniinae have evolved independently several times within the tribe. However, only one pollen type is found in many © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159, 155–162 PALYNOLOGY OF THE SUBTRIBE PITHECOCTENIINAE 159 Table 3. Pollen measurements (mm) for species with inaperturate, spheroid pollen type (standard deviation in parentheses) Species Diameter Ektexine Endexine Distictella cuneifolia Da. dasytricha Da. elongata Da. laevis Da. parkeri Da. magnoliifolia Da. mansoana Da. monophylla Da. obovata Da. reticulata Distictis buccinatoria D. granulosa D. lactiflora D. laxiflora D. pulverulenta D. staminea Pithecoctenium crucigerum P. cynanchoides P. dolichoides P. hatschbachii 71.4 59.6 65.3 65.2 68.5 61.4 62.9 66.3 64.9 70.3 54.7 66.7 56.2 51.9 59.5 45.1 67.6 61.1 61.4 67.9 5.8 5.2 5.5 4.4 5.1 5.3 4.6 4.4 5.6 5.6 4.2 5.2 4.4 3.9 4.8 3.6 4.9 4.7 4.5 5.2 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1.7 (0.5) 1 (0) 1 (0) 1.6 (0.5) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) (3.7) (2.9) (4.9) (6.8) (4.7) (4) (6.9) (9.5) (4.2) (4.9) (3.7) (6) (4.3) (2.0) (5.3) (5.5) (5.8) (6) (8.7) (7.8) (0.5) (0.7) (5) (0.8) (0.8) (0.7) (0.5) (0.5) (0.5) (0.5) (0.6) (0.9) (0.5) (0.4) (0) (0.5) (0.5) (0.5) (0.6) (0.4) µm 120 100 80 60 40 H. glaziovii H. bracteatum H. rodriguesii G. bauhiniodes A. pan. var molle A. paniculatum A. pan. var. imata A. ecuadorense A. blanchetii A. sandwithii A. aschersonii A. perbactreatum Da. mansoana Da. obovata Da. cuneifolia Da. dasytricha Da. parkerii Da. monophylla Da. laevis Da. magnoliifolia Da. reticulata Da. elongata D. staminea D. lactiflora D. laxiflora D. buccinatoria D. granulosa D. pulverulena P. dolichoides P. cynanchoides P. hatschbachii P. crucigerum 20 Figure 9. Equatorial diameter dimensions of pollen in Pithecocteniinae. of the 21 species groups (genera) recognized by Lohmann (2006). Thus, in the sister clade of Pithecocteniinae, we find Anemopegma, Mansoa and Pyrostegia with stephanocolpate, perisyncolpate and tricolpate pollen types, respectively. Except for Potamoganus and Roentgenia, most of the so-called ‘mimetic clade’ in the sister group has inaperturate pollen (Lohmann, 2006). In the case of Pithecocteniinae, the clade formed by Amphilophium, Glaziovia and Haplolophium has stephanocolpate pollen. Genera with inaperturate pollen do not appear to constitute a monophyletic group. However, whether or not Distictis © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159, 155–162 160 C. M. BURELO-RAMOS ET AL. Figures 10–18. Exine sculpturing of stephanocolpate pollen in Pithecocteniinae. Figs 10–12. Amphilophium paniculatum var. molle. Fig. 10. ¥1500; scale bar, 10 mm. Fig. 11. ¥1300; scale bar, 10 mm. Fig. 12. ¥6000; scale bar, 3 mm. Figs 13–15. A. paniculatum var. paniculatum. Figs 13, 14. ¥1500; scale bar, 10 mm. Fig. 15. ¥3700; scale bar, 5 mm. Figs 16–18. A. ecuadorense. Fig. 16. ¥1500; scale bar, 10 mm. Fig. 17. ¥1200; scale bar, 10 mm. Fig. 18. ¥8000; scale bar, 2 mm. and Pithecoctenium conform to a monophyletic unit does not change the view of character evolution in this case: stephanocolpate pollen derives from the inaperturate type in Pithecocteniinae. In addition to the pollen type, Amphilophium, Glaziovia and Haplolophium share other characters, such as definitely lobed calices, seed wings glabrous and tracheary elements of the wings without secondary thickenings. However, although Distictella, Distictis and Pithecoctenium do not form a monophyletic group, they share truncate to denticulate calices, puberulent seed wings and tracheary elements of the wings with spiral secondary thickenings. In addition, Distictella is distinguished by the presence of cylindrical stems, and Pithecoctenium by the presence of tendrils successively several times trichotomic. In the molecular phylogenetic study of Bignonieae, Lohmann (2006) obtained a strongly supported clade equivalent to the group called, in this article, Pithecocteniinae. Beyond this point, except for the Dis- tictella species, her analysis did not identify monophyletic groups corresponding to the genera currently included in the subtribe. Considering this, and putative morphological synapomorphies, she suggested to lump all the species of the subtribe into a single genus. We believe, however, that morphology, such as pollen features, can still provide additional characters to evaluate possible monophyletic groups within this aggregate of species, which might support some of the genera currently included in Pithecocteniinae. ACKNOWLEDGEMENTS We are grateful to the Instituto de Ecología, A. C. and the following organizations for funding of the doctoral studies of the first author: Consejo Nacional de Ciencia y Tecnología (CONACyT; scholarship number 157797) and the Universidad Juárez Autónoma de Tabasco for support through the 2002 Institutional © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159, 155–162 PALYNOLOGY OF THE SUBTRIBE PITHECOCTENIINAE 161 Figures 19–27. Exine sculpturing of stephanocolpate pollen in Pithecocteniinae. Figs 19–21. Glaziovia bauhinioides. Figs 19, 20. ¥1500; scale bar, 10 mm. Fig. 21. ¥9000; scale bar, 2 mm. Figs 22–24. Haplolophium rodriguesii. Figs 22, 23. ¥1600; scale bar, 10 mm. Fig. 24. ¥7000; scale bar, 2 mm. Figs 25–27. H. glaziovii. Figs 25, 26. ¥1500; scale bar, 10 mm. Fig. 27. ¥9000; scale bar, 2 mm. Table 4. Pollen measurements (mm) for species with stephanocolpate, prolate pollen type (standard deviation in parentheses) Species Polar length Equatorial length Ektexine Endexine Amphilophium aschersonii A. blanchetii A. ecuadorense A. paniculatum var. paniculatum A. paniculatum var. imatacense A. paniculatum var. molle A. perbracteatum A. sandwithii Glaziovia bauhinioides Haplolophium bracteatum H. glaziovii H. rodriguesii 64.3 (4. 1) 52.8 (4.3) 53.3 (4) 59.5 (5.5) 54.7 (3.9) 53.5 (4.4) 70.6 (4.5) 63.9 (3.9) 57 (4.9) 59.2 (6.1) 81 (4.6) 49.6 (3.7) 68.3 68.9 67.5 60.1 69.8 61.4 78.8 68.6 68.9 82.6 82.4 71.9 4.9 (0.7) 5.6 (0.9) 5 (0.9) 5.1 (0.7) 4.8 (0.8) 5.2 (0.5) 3.9 (0.7) 5.3 (0.2) 5.2 (0.5) 7.6 (0.5) 5.3 (0.5) 4.8 (0.37) 1.2 (0.4) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1 (0) 1.2 (0.4) 1.3 (0.5) 1.12 (0.3) 1.3 (0.5) 1 (0) (5.6) (5.9) (5.8) (3.7) (6.2) (5.2) (7.1) (6.1) (5.1) (5.3) (12.8) (3.5) © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159, 155–162 162 C. M. BURELO-RAMOS ET AL. µm 95 85 75 65 55 45 35 25 H. glaziovii H. rodriguesii A. molle A. imatacense A. blanchetii A. aschersonii H. bracteatum G. bahuinioides A. paniculatum A. ecuadorense A. sandwithii A. perbactretum Figure 28. Polar diameter dimensions of prolate pollen in Pithecocteniinae. Academic Advancement Programme. We thank the following herbaria for the loan of specimens and for the use of their facilities during visits: COL, ESAL, F, HB, HUEFS, MBM, NY, R, SP, UEC, UJAT, VEN and XAL. Thanks go to an anonymous reviewer for a critical review of the manuscript. Tiburcio Laez Aponte operated the scanning electron microscope and Maricruz Peredo Nava edited the figures. REFERENCES Bove CP. 1993. Pollen morphology of the Bignoniaceae from a south Brazilian Atlantic forest. Grana 32: 330–337. Bove CP. 1994. Morfologia polínica de Bignoniaceae (lianas) do Brasil meridional. Revista Brasil Biology 54: 273– 291. Buurman J. 1977. 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Berichte der Deutschen Botanischen Gesellschaft 34: 728– 758. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159, 155–162