Pollen morphology of Xanthium L. (s.l.) (Asteraceae, Asteroideae, Heliantheae, Ambrosiinae) in the Iberian Peninsula - a palynotaxonomic approach to a poisonous, allergenic and invasive genus

Abstract

The pollen morphology of the Iberian taxa of the genus Xanthium s.l. and of the non-Iberian species X. ambrosioides was studied to help to identify these poisonous, allergenic and invasive taxa and clarify their taxonomic relationships. In addition, the question of the existence and structure of a mesoaperture in the apertural system of Xanthium was also considered. The pollen grains of sections Acanthoxanthium and Xanthium clearly differ by their characters, which supports the separation of both taxa and allows for their distinction based on pollen morphology. It is suggested that the morphological and palynological differences between Xanthium and Acanthoxanthium, together with the lack of hybridisation between the two sections and the monophyly of Acanthoxanthium, could lead to the elevation of the latter to the generic status. The two species of section Xanthium present in the Iberian Peninsula (X. orientale and X. strumarium) and of section Acanthoxanthium are well separated by their palynological features. Likewise, the Iberian subspecies of Xanthium, X. orientale subsp. orientale and X. orientale subsp. italicum are palynologically distinguishable. However, no significant difference could be found between the pollen of X. strumarium subsp. strumarium and of X. strumarium subsp. brasilicum. The pollen data do not support the hypotheses of a hybrid origin for X. strumarium subsp. brasilicum. A mesoaperture intersecting the foot layer and the upper part of the endexine is present in both sections, which is congruent with the results already found for other Asteroideae.

Keywords:

• exine
• light microscopy (LM)
• scanning electron microscopy (SEM)
• transmission electron microscopy (TEM)
• principal component analysis (PCA)
• t-test

Acknowledgements

The authors are grateful to the curators of E, MA, PO, SALA, SEV and to the late curator of COI, Dr. Teresa Almeida for having allowed the pollen removal of the vouchers. Also, we thank Mónica Zuzarte (IBILI, Coimbra, Portugal) for her very helpful work with TEM. This work was supported by the “Fundação para a Ciência e a Tecnologia” [UID/BIA/04004/2020]; “Quadro de referência estratégica nacional” (QREN) [ICT_2009_02_012_1890]. Acknowledgement is also due, to the financial support from FCT (MCTES) to CESAM (UIDP/50017/2020+UIDB/50017/2020), through national funds.

Disclosure statement

No potential conflict of interest was reported by the authors.

Specimens Investigated

The type of microscopy is indicated between square brackets:

Section Acanthoxanthium

Xanthium spinosum DC. subsp. spinosum. Portugal: Alto Alentejo, Elvas, 12. VII. 1979, J. A. Guerra 1424 (MA 247704) [LM, SEM, TEM]; Douro Litoral, Vila Nova de Gaia, Oliveira do Douro, Pedra Bela 7. X. 1966, Costa & Araújo s. n. (PO 23882) [LM, SEM]. Spain: Barcelona, lit du Besós, 16. VIII. 1921, F. Sennen 4200 (MA126446) [LM, SEM]; Jáen, Baños de la Encina, 25. X. 1987, J. A. González Carmona s. n. (SEV 266265) [LM, SEM]; La Rioja, Ojacastro, 26. VIII. 1999, G. García Baquero 834 (SALA 99025) [LM, SEM, TEM]; Sevilla, la Pañoleta, 13. VIII. 1974, S. Silvestre s. n. (MA 358291) [LM, SEM]; Valladolid, Renedo de Esgueva, 12. VIII. 2000, Jesús Antonio Lázaro Bello s. n. (SALA 112913) [LM, SEM].

Xanthium ambrosioides Hook. & Arn. United Kingdom: San Luis, s. d., s. coll. (E 00322788) [LM, SEM, TEM]; Bedford, M. M. Callum Webster 8197 (E 00451728) [LM, SEM, TEM].

Section Xanthium

Xanthium orientale L. subsp. italicum (Moretti) Greuter Portugal: Alto Alentejo, Elvas, Ajuda, 28. IX. 1956, A. Raimundo & J. A. Guerra 3646 (MA 247693) [LM, SEM, TEM]; Beira Litoral, Coimbra, Gorgolão, 23. IX. 1970, A. Queirós s. n. (COI) [LM, SEM]. Spain: Alicante, L’Alcoiá, 7. IX. 1986, J. R. Nebot s. n. (MA 403999) [LM, SEM]; Barcelona, Can Tunis, 17. X. 1912, F. Sennen 1494 (MA 126389) [LM, SEM]. Huelva, Puerto de la Laja, 19. VIII. 2007, J. Calvo s. n. (MA 773476) [LM, SEM]; Pontevedra, Crecente, 4. IX. 2004, J. Amigo s. n. (MA 792574) [LM, SEM]; Toledo, Talavera de la Reina, 8. VIII. 2004, F. Mario Sanz Elorza s. n. (MA 751345) [LM, SEM, TEM].

Xanthium orientale L. subsp. orientale Portugal: Estremadura, próximo ao Samouco, IX. 1883, António Xavier Pereira Coutinho s. n. (COI) [LM, SEM]. Spain: Ávila, El Barraco, 30. IX. 2009, M. Sanz Elorza s. n. (MA 846772) [LM, SEM, TEM]; Oviedo, Morcín, Santa Eulalia, 30. IX. 1972, F. Navarro s. n. (SALA 70765) [LM, SEM]; Salamanca, Pelabravo, 19. IX. 1980, E. Rico, J. M. Velasco & A. Pastor s. n. (SALA 58590) [LM, SEM]; Segovia, Navalilla, 10, X. 1984, T. Romero s. n. (SALA 39903) [LM, SEM]; Toledo, Algodor, 30. VIII. 1925, A. Caballero & G. Guerrero s. n. (MA 126380) [LM, SEM]; Valladolid, Cigales. 3. IX. 2007, J. A. Lázaro Bello s. n. (MA 791465) [LM, SEM, TEM].

Xanthium strumarium L. subsp. brasilicum (Vell.) O. Bolòs & Vigo Spain: Barcelona, lit du Besós, 16. VIII. 1921, F. Sennen 4198 (MA 126413) [LM, SEM]; Cáceres, Navalmorel, 23. X. 1983, Ruíz Téllez s. n. (SALA 68034) [LM, SEM]; Cuenca, Cañete, 22. IX. 1974, S. Boudía, A. González & G. López 1248 GF (MA 442034) [LM, SEM]; Huelva, El Granado, 10. X. 1996, C. Santa Bárbara & B. Valdés s. d. (SEV 147448) [LM, SEM, TEM]; Murcia, Cartagena, 25. VIII. 1901, Francisco Jiménez s. n. (MA 126405) [LM, SEM]; Zaragoza, Calatayud, 26. VIII. 1910, C. Vicioso s. n. (MA 126404) [LM, SEM]; Zamora, Toro, 10. VIII. 1993, J. M. Velasco s. n. (SALA 58646) [LM, SEM, TEM].

Xanthium strumarium L. subsp. strumarium Portugal: Beira Litoral, Coimbra, Paúl de S. Fagundo, VII. 1878, M. Ferreira s. n. (COI) [LM, SEM]. Spain: Alicante, Saladares de las Virtudes, 26. VIII. 1961, A. Rigual s. n. (MA 369937) [LM, SEM]; Cataluña, environs Figueras, 21. X. 1904, F. Sennen s. n. (MA 126477) [LM, SEM]; Córdoba, Morrachuelos, 20. X. 1980, Fernández & Porras s. n. (SEV 242773) [LM, SEM]; Jáen, Santiago de la Espada, 16. IX. 1987, S. Talavera & B. Valdés s. n. (SEV 235907) [LM, SEM, TEM]; La Rioja, Logroño, VII. 1984, Rubia s. n. (MA 126409) [LM, SEM, TEM]; Madrid, Aranjuez, 19. IX. 1975, S. Cirujano s. n. (MA 246464) [LM, SEM].

Additional information

Funding

This work was supported by the Fundação para aCiência e a Tecnologia [through UID/BIA/04004/2020 and UIDP/50017/2020+UIDB/50017/2020].