Abstract
The distinction of the annual Sagina apetala and S. micropetala (= S. apetala subsp. erecta, S. filicaulis) is based mainly on the position of sepals in fruit and shape and colour of the sepals, but identification of the two species is difficult. A molecular phylogeny of material identified as S. apetala and S. micropetala as well as other species of the genus using two nuclear and two plastid markers showed that there exist two lineages that are sister to each other and can be unambiguously distinguished molecularly. Although many of the morphological characters used in the literature proved useful in distinguishing these two lineages, sepal indumentum is the most reliable character to discriminate between them in Germany. Whereas S. micropetala usually has glabrous sepals, the sepals of S. apetala usually are glandular-pubescent. The chromosome number of 2n = 12 for S. micropetala, here determined for the first time, is identical to that of S. apetala, supporting the close relationship between the two species. Sagina apetala and S. micropetala are sister to S. maritima, an annual species from European coasts, which may imply a coastal origin of the two species. A brief review of the possible origin of other European ruderals from coastal relatives is provided. Citation: Dillenberger M. S. & Kadereit J. W. 2022: The distinction between Sagina apetala and S. micropetala (Caryophyllaceae: Sagineae), their phylogenetic relationships, and a note on the coastal origin of some widespread ruderals. – Willdenowia 52: 5–23. Version of record first published online on 10 February 2022 ahead of inclusion in April 2022 issue.
Highlights
Sagina L. of tribe Sagineae (Caryophyllaceae) is a predominantly northern hemisphere genus of c. 33 species (Bittrich 1993; Alban & al. 2022)
As we found that S. apetala and S. micropetala are closest relatives of the coastal S. maritima, we will briefly discuss the possibly coastal origin of S. apetala and S. micropetala as well as of other widespread European ruderals
Our phylogenetic analysis of material provisionally identified as Sagina apetala and S. micropetala revealed the existence of two distinct and well-supported lineages that are sister to each other and closest relatives of the morphologically similar S. maritima
Summary
Sagina L. of tribe Sagineae (Caryophyllaceae) is a predominantly northern hemisphere genus of c. 33 species (Bittrich 1993; Alban & al. 2022). The only perennial species among the tetramerous taxa is S. procumbens L., the type species of the genus. This species is a common weed typically growing in pavement cracks and has been introduced to different parts of the world (e.g. the Americas; Crow 2005). Apart from being perennial, S. procumbens can be distinguished from other tetramerous species by the presence of a persistent basal leaf rosette, its procumbent growth, and pedicels curved downward after anthesis (Jäger 2011). The remaining tetramerous species, i.e. S_apetala Ard., S. maritima Don and S. micropetala Rauschert, are erect, have basal leaf rosettes that wither quickly, pedicels that remain erect after anthesis (Jäger 2011), petals present only rarely, and anthers open when flowers open The remaining tetramerous species, i.e. S. apetala Ard., S. maritima Don and S. micropetala Rauschert, are erect, have basal leaf rosettes that wither quickly, pedicels that remain erect after anthesis (Jäger 2011), petals present only rarely, and anthers open when flowers open (pers. obs.)
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