A Revised Taxonomy of the Bassia scoparia Complex (Camphorosmoideae, Amaranthaceae s.l.) with an Updated Distribution of B. indica in the Mediterranean Region

Abstract

Bassia scoparia is a widespread weedy species in the temperate regions of the world and is valued as a medicinal and ornamental plant. To date, the taxonomic concept of B. scoparia remains insufficiently studied due to a limited number of samples used in the previous phylogenetic analyses. To solve the taxonomy of the B. scoparia complex, we constructed a new phylogeny based on the nuclear ribosomal internal transcribed spacer (ITS), plastid intergenic spacer atpB-rbcL, and plastid region rpL16 intron sequences for numerous samples with diverse morphology. Our analysis revealed a close proximity and intermixed positions of the samples of the B. scoparia group with various morphology. Because of this polyphyly, we prefer to broadly delimit the species. An updated nomenclature of B. scoparia is provided including four new synonyms: Bassia angustifolia, B. littorea, Kochia albovillosa, and K. scoparia subsp. hirsutissima. In its new circumscription, B. scoparia encompasses populations with glabrous or variously hairy leaves and perianths. The original material of Kochia sieversiana, previously considered a species with hairy leaves and inflorescences, has the same diagnostic characters as in B. scoparia s.str. The correct name for more hairy-leaved plants is B. scoparia var. subvillosa. Plants with hairy perianths known as Kochia albovillosa and K. scoparia subsp. hirsutissima have a restricted distribution in Central Asia and South Siberia and have never been recorded as alien in other regions; they can be classified as a separate variety, B. scoparia var. hirsutissima. The ornamental variant of oblong or pyramidal shape may be called B. scoparia var. trichophila. Bassia scoparia is often confused with a similarly looking relative, B. indica, especially in North Africa, a region where secondary ranges of both species overlap. Phylogenetically, these species are sister groups; they share some morphological characters but have different primary distribution ranges. We traced a recent expansion of B. indica in the Mediterranean with the first record reported from the European continent (Spain) and uncovered various introduction pathways of the species in this region.

Keywords: Amaranthaceae; Bassia; Mediterranean; classification; distribution; molecular phylogeny; plant invasion; taxonomy.

Figure 1

Phylogeny of Bassia and outgroups, recovered from the partitioned Maximum Likelihood (ML) analysis of the concatenated dataset (ITS, atpB-rbcL intergeneric spacer, and rpL16 intron) and presented as a cladogram. Numbers above or below branches indicate ML aLRT support values [21]. The figure shows only clades that received aLRT support higher than 0.8. An asterisk denotes the clade corresponding to the B. scoparia taxonomic alliance.

Figure 2

Distribution of Bassia indica in the Mediterranean. Each color indicates first records, namely, red 1910+ (Israel/Palestine), orange 1930+ (Egypt), yellow 1950+ (Syria), bright green 1960+ (Algeria), dark green 1970+ (Libya), light blue 1990+ (Cyprus), dark blue 2000+ (Morocco, Tunisia), and violet 2020+ (Spain). Black dots indicate records based on the herbarium specimens, empty dots indicate records taken from [36].

Figure 3

Bassia indica in Spain. (A) B. indica in Vila-real, 29 August 2023. The species has a typical tumbleweed habit. (B) The typical dense stem indumentum of B. indica (Vila-real, 30 August 2023). (C) B. indica on bare, sunlit, and stony ground at the railway station of Vila-real, 30 August 2023. (D) Inflorescence of B. indica in Vila-real, 11 September 2023. Photographs by F. Verloove.

Figure 4

Bassia scoparia var. trichophila. (A) Ornamental cultivation in Penza City, Russia (August 2023, photographer A. Sukhorukov); (B) escaped from cultivation (Morocco, 17 December 2023, photographer J.-F. Léger).

Figure 5

Records of Bassia scoparia with pubescent perianths (previously known as Kochia albovillosa or K. scoparia subsp. hirsutissima).