No abstract

Using optical and scanning electron microscopy, we completed a palynological study of the subtribe Artemisiinae (Asteraceae, Anthemideae), which we started in a previous paper. This subtribe contains different genera with a systematic position that, in many cases, has been controversial. There is a group of genera closely related to Artemisia, and another one more related to Chrysanthemum sensu lato. We confirm the existence of two pollen morphological patterns ‐ concerning exine ornamentation ‐ in the tribe Anthemideae and in the subtribe Artemisiinae as currently considered: one with long spines (Anthemis type) and the other with short spinules (Artemisia type). This feature is a good taxonomic marker, well correlated with other morphological and with molecular characters. This enables a new delimitation of the subtribe Artemisiinae, which is characterized by pollen grain ornamentation constituted by short spinules (microechinate pollen), and should be restricted to Artemisia and the closely related genera that share this trait.

Using optical and scanning electron microscopy, we carried out a palynological study of some plant species with a systematic position that has been controversial. One of the taxa belongs to the genus Artemisia (Asteraceae, Anthemideae), but has been described in another genus (Artemisia incana/Tanacetum incanum). The remaining taxa have been named or combined in Artemisia but are now considered members of small genera mostly segregated from Artemisia (Ajania, Hippolytia, Kaschgaria, Lepidolopsis, Mausolea, Turaniphytum), or belong to very close genera (Brachanthemum, Sphaeromeria). We confirm the existence of two pollen morphological patterns ‐ concerning ornamentation ‐ in the tribe Anthemideae: one with long spines (Anthemis type) and the other with short spinules (Artemisia type). Artemisia and its related genera can also be divided into two groups according to this feature, which is a good taxonomic marker, well correlated with other morphological and molecular characters.

The natural status of the genus Plectocephalus is confirmed and several nomenclatural combinations are proposed. New evidence contributes to the debate concerning problems posed by the use of ITS in the phylogenetic reconstruction of groups that differ in terms of their life cycles. Dispersal from Caucasus and Anatolia along the Siberian route and then across the Bering Land Bridge follows a route previously proposed for other taxonomic groups.

Hybridization has played an important role in Saxifraga evolution causing reticulation and a high number of described hybrids, but little is known about how hybrid speciation had occurred in the genus. We focus on a group of closely related Saxifraga species of the subsection Triplinervium from Pyrenees, the phylogenetic relationships of which remain unsolved. Trying to unmask cryptic (or ancient) hybridization processes, we analyze one nuclear (ITS) and three plastid regions (rpl32‐trnL, trnS‐trnG‐trnG, and 3′trnV‐ndhC), as well as nuclear DNA content. Pollen and seed morphology and viability studies were carried out to evaluate the status of spontaneous hybrids. DNA ploidy levels were also inferred for the two Madeiran taxa (of the same Saxifraga subsection), where recent hybridization processes are not expected. Molecular markers revealed multiple reticulation events, which, as suggested by DNA content and chromosome numbers, have occurred in homoploidy (without genome doubling after hybridization). In addition, autopolyploidy has occurred in some species or populations, especially in the Madeiran archipelago colonization. Chromosome number variation appears to be related to centric fission events, which also could lead to the formation of the B chromosomes inferred in some taxa. Spontaneous hybrids do not produce viable seeds and this could be due to differences in parental chromosome numbers. Hybrid speciation has probably been successful by chromosomal arrangements, which also generated new, more or less intermediate, chromosomal numbers in this group of taxa.