Systematics, biogeography and apomixis in Elatostema (Urticaceae)
Date Issued
2016
Date
2016
Author(s)
Tseng, Yu-Hsin
Abstract
Elatostema (Urticaceae), consisting of about 500 species, is mainly distributed in the tropical to subtropical areas with a diversity center in tropical Asia. Elatostema has long been a taxonomically difficult group due to frequent homoplasy of morphological characters and numerous species with a wide distribution and complex sexual systems. The circumstances of generic delimitation among Elatostema, Elatostematoides, Pellionia and Procris are quite controversial, and the infrageneric grouping within Elatostema is also uncertain. A taxonomic revision of Elatostema in Taiwan was carried out based on field observation, careful examination of specimens and molecular phylogeny. The first natural hybrid in Urticaceae, E. ×hybrida, was confirmed, which is derived from natural hybridization events between E. lineolatum var. majus (♀) and E. platyphyllum (♂). So far, we recognize 15 species and one natural hybrid in Taiwan. A comprehensive phylogenetic analysis, comprising Elatostema and related Urticaceae taxa (Elatostematoides, Pellionia, and Procris), was conducted. The results showed that Elatostema s.l. can be divided into three well-supported genera: Procris, Elatostematoides and Elatostema s.a. Four strongly support subclades within Elatostema s.a. can be recognized, including Weddellia clade, Pellionia clade, Afroelatostema clade and core Elatostema clade. Homoplasy amongst the morphological characters used in this study makes it impossible to circumscribe genera using synapomorphies. Combined suites of characters, however, do enable the morphological diagnosis of Elatostema s.l. The evolutionary history of Elatostema s.a. involves in a variety of biogeographical scenarios. Two intercontinental dispersal events from Asia to Africa were identified, which are probably correlated with two warm phases peaking during Cenozoic Era, respectively. There are at least five major dispersal events within core Elatostema clade, including the two routes of origin from East Asia through Malesia to Australasia. Besides, a strong association between geography and phylogenetic relationship was recovered within Afroelatostema and core Elatostema clades, which may attribute to limited dispersal mechanism. Furthermore, limited gene flow may be an important feature in speciation and evolution in Elatostema s.a. In addition, based on previous field observation, E. cyrtandrifolium, E. oblongifolium and E. rivulare only have female individuals or female-biased species and still can produce seeds. In this study, these species are confirmed to be apomictic plants with polyploidy. The results of flow cytometric seed screen and embryogenesis further demonstrated that these species should belong to an infrequent case of obligate autonomous apomixis.
Subjects
apomixis
Elatostema
evolutionary history
inter- and infrageneric relationship
molecular phylogeny
morphology
taxonomic revision
Urticaceae
Type
thesis