The unique type of pollen grain of Dasistoma (Macranthera-Agalinis clade; Orobanchaceae): implications for taxonomy

Abstract

Pollen morphology of six species from the Macranthera-Agalinis clade (Orobanchaceae) was studied using both light microscopy and scanning electron microscopy. Pollen grains are (2-)3(4-)-colpate, 3-brevicolpate and 4-, rarely 6-porate, obtate to prolate (P/E = 0.72–1.52) in shape; medium-sized and rarely large-sized (P = 26.60–50.54 µm, E = 22.61–47.88 µm). Three pollen types are found and described based on the pollen grain size, length of the colpi, exine thickness, exine sculpture, columellae length and thickness and nanogemmae size. Type III contains three subtypes differentiated by pollen grain size, length of the colpi, exine thickness, exine sculpture, columellae length and nanogemmae size. Unweighted pair group method with arithmetic mean (UPGMA) dendrograms based on palynological data support that Dasistoma macrophylla has unique morphological and morphometric characters. In D. macrophylla we observed a transition from the 3-brevicolpate type to the 4-porate and occasionally 6-porate type. This polymorphism with respect to apertures may provide an advantage for D. macrophylla to survive under different ecological conditions and on a wide range of hosts. Palynomorphological data are interpreted in the existing phylogenetic framework. The 3-colpate type of apertures and a nanogemmate exine sculpture are hypothesised to be the plesiomorphic condition within the Macranthera-Agalinis clade.

Keywords:

• exine sculpture
• diagnostic features
• phylogeny
• taxonomy
• SEM-analysis

Acknowledgements

The authors express their gratitude to James C. Solomon, Head Curator of the Missouri Botanical Garden Herbarium (MO – St Louis, Missouri, USA), Natalia M. Shyian, Head Curator of the National Herbarium of Ukraine (KW – herbarium of the M.G. Kholodny Institute of Botany, National Academy of Sciences of Ukraine). Kind help and cooperation of Dmytro O. Klymchuk, Head of the Centre of Electron Microscopy (M.G. Kholodny Institute of Botany, National Academy of Sciences of Ukraine), are greatly appreciated. The authors are very grateful to Gerald M. Schneeweiss (University of Vienna, Austria) for his valuable comments and critically reading and substantially improving the manuscript. The authors also thank Elsa Marie Friis, editor-in-chief of the journal, and anonymous reviewers for valuable comments and suggestions.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Specimens investigated

Agalinis tenuifolia (Vahl) Raf. – Plant of Arkansas. Coll. by Delzie Demaree Hempstead County. Low marl ridges. Common. Elevation fl. 380. P.O. Blevins. 12 October 1964. (KW009470).

Aureolaria pedicularia (L.) Raf. ex Farw. – Herbarium of P.O. Schallert, M.D. Winston-Salem, N.C., U.S.A. Teulon. 23 October 1932. (KW).

Dasistoma macrophylla (Nutt.) Raf. – Plants of Missouri, USA. Crawford County: Onondaga Cave State Park, along Blue Heron Trail.; Base of bluffs. 38.03.32 N 091.13.41 W 650 ft. S.R. Turner. 31 July 2014. 14–149. (MO).

Esterhazya splendida J.C. Mican – Province of Goyaz, Brazil. George Gardner. Turczaninow historical herbarium (KW-TURCZ) (two specimens).

Macranthera flammea (W. Bartram) Pennell – 1. Hancock County. Herbarium F.H. Sargent. Locality: Picayune, Miss., 10 mi. SE of. 17 August 1969. 9885 (MO). 2. Florida. Chapman. Turczaninow historical herbarium (KW-TURCZ).

Seymeria cassioides (S.F. Gmel.) S.F. Blake – 1. In montibus Caroline et Georgie. Leg. S.B. Buckley. Turczaninow historical herbarium (KW-TURCZ). 2. Florida. Chapman. Turczaninow historical herbarium (KW-TURCZ).