Introduction
The legume tribe Genisteae (Papilionoideae, Fabaceae) comprises 25 genera and 7 subtribes. Recent phylogenomic and molecular study employing extensive sampling and high-throughput sequencing has robustly resolved the long-debated generic relationships within Genisteae into four major, strongly supported clades: the Cytisus–Genista complex, the Lupinus clade, the Anarthrophyllum group and the Argyrolobium group, the latter being the earliest diverging lineage within Genisteae (Hunter et al. Reference Hunter, Cardoso, Ruhlman and Jansen2025). This group includes Argyrolobium, Dichilus and Melolobium, which share a two-lipped calyx with a trifid lower lip (Edwards Reference Edwards2005). While Melolobium and Dichilus are consistently resolved as monophyletic based on morphological, phytochemical (alkaloid profile) and molecular evidences, Argyrolobium remains problematic due to extensive morphological variation, overlapping traits and poorly described protologues, all of which complicate species delimitation and generic circumscription (Edwards Reference Edwards1994, Reference Edwards2005; Käss and Wink Reference Käss and Wink1997; Kajita et al. Reference Kajita, Ohashi, Tateishi, Bailey and Doyle2001; Ainouche et al. Reference Ainouche, Bayer, Cubas and Misset2003; Le Roux and Boatwright Reference Le Roux and Boatwright2023).
Argyrolobium comprises nearly c. 97 species distributed across Africa, Madagascar, Mediterranean and Asia, including India (Edwards Reference Edwards2005). Its broad distribution has hindered comprehensive phylogenetic analyses, which so far have remained largely regional. Molecular phylogenetic studies based on ITS and plastid markers (rbcL, matK, trnL–F) have focused almost entirely on South African species (SA spp.), with minimal representation from Eurasia and Mediterranean, and no inclusion of Asian representatives (Käss and Wink Reference Käss and Wink1997; Kajita et al. Reference Kajita, Ohashi, Tateishi, Bailey and Doyle2001). During collection tours in the north-western Himalayan region of India, the author collected an interesting specimen of Argyrolobium. Detailed morphological examination and comparison with relevant taxonomic literature identified it as Argyrolobium roseum (Cambess.) Jaub. & Spach. Subsequent literature survey indicated that, although A. roseum is morphologically distinct from the SA Argyrolobium assemblage, its phylogenetic position relative to SA spp. has never been evaluated using molecular data. This omission represents an important gap in current phylogenies, which consistently recover Argyrolobium as paraphyletic and remain incomplete due to limited geographic sampling. Therefore, the present study provides the first molecular characterization of A. roseum from India using ITS and rbcL sequences to test whether A. roseum clusters with SA spp. or instead shows affinities with Mediterranean lineages or the Cytisus–Genista complex.
Experimental
Sampling
A. roseum was collected from India (Jammu and Kashmir) during field trips in 2021. Species identification was done by consulting protologue, taxonomic literature and specimens housed at G, E, K and MPU. Diagnostic features were verified with photographic documentation (Figures S1, S2, Table 1). To compare morphology across major biogeographic groups, data were extracted from protologue, floras, taxonomic treatments and the present study. This literature-based comparison was used to identify and summarize key morphological characters separating A. roseum from its African and Mediterranean congeners (Table 1).
Comparative morphological characters of Argyrolobium species from different geographic regions
Table 1 Long description
The table compares diagnostic morphological traits across three named Argyrolobium species from Southwest Asia and the Mediterranean–North Africa region and a summary profile for South African species. It lists geographic distribution, growth habit, height, leaflet shape and hairiness, stipules, inflorescence type and flower number, corolla and standard petal hairiness, legume size, and seed number. The three non South African species are low, mostly prostrate to tufted subshrubs or herbs, typically about ten to forty centimeters tall, with small stipules and inflorescences ranging from solitary to about five flowers. South African species span herbs to shrubs, commonly about fifteen to sixty centimeters tall and sometimes reaching about one meter, and show the widest range of leaflet shapes and stipule forms, including large or even leaflike stipules in one lineage. Leaf hairiness is consistently stronger on the lower surface in the South African group, while the other species range from nearly hairless above with sparse hairs below to silky on both surfaces. Flower color is broadly yellow across all groups, but South African species can show orange to reddish tinges and may darken when damaged, and standard petals vary from hairless to hairy depending on species. Fruits are generally larger in the South African group, with legumes commonly around thirty to sixty millimeters and sometimes much longer, and they tend to contain more seeds than the three compared species. Values for the South African column summarize multiple species, so ranges reflect within region diversity rather than a single taxon.
Data compiled from protologue, regional floras, taxonomic revisions and present study.
Phylogenetic analyses
All available ITS and rbcL sequences for members of Argyrolobium (Argyrolobium, Dichilus, Melolobium) and Anarthrophyllum group (Polhillia, Anarthrophyllum, Sellocharis) were downloaded from GenBank (Table S1). ITS sequences of Argyrolobium armindae, A. abyssinicum, A. lunare, Dichilus lebeckioides and D. pilosus were excluded due to incompleteness or numerous unresolved bases. Representative taxa from Cytisus–Genista and Lupinus clades were added to cover the four major Genisteae lineages (Hunter et al. Reference Hunter, Cardoso, Ruhlman and Jansen2025). Members of Lupinus clade served as outgroup. DNA extraction, PCR, sequencing (ITS and rbcL) and phylogenetic analyses (RAxML v.8.1.18 and MrBayes v.3.2.7) were done as described previously (Fay et al. Reference Fay, Swensen and Chase1997; Mittal and Dangi Reference Mittal and Dangi2025, Table S2).
Discussion
The ITS-I, ITS-II and rbcL regions of the newly sequenced A. roseum were 224, 220 and 692 bp in length, respectively. In the ITS tree (Figure S3) generic circumscription of Polhillia, Dichilus and Melolobium in the Argyrolobium + Anarthrophyllum group was fully supported. The clade uniting Anarthrophyllum and the closely related monotypic genus Sellocharis was supported moderately. Argyrolobium was paraphyletic due to the placement of A. zanonii, A. uniflorum and A. roseum outside the clade formed by SA spp. The clade uniting A. uniflorum with A. roseum, Melolobium and Dichilus lacked support. The rbcL trees were poorly resolved because of fewer parsimony informative sites (Figure S4). In the rbcL tree, Argyrolobium was paraphyletic, but the clade uniting A. uniflorum, A. roseum, Dichilus and Melolobium was well supported.
Although concatenated dataset included fewer taxa due to missing rbcL sequences, all genera of Argyrolobium + Anarthrophyllum group were represented. No strongly supported incongruence was detected between nuclear and plastid-derived phylograms, suggesting that missing rbcL sequences for some taxa are unlikely to have substantially influenced the overall concatenated topology. In agreement to ITS analysis, combined analysis also resolved members of Genisteae into three clades: Anarthrophyllum + Argyrolobium group, the Cytisus–Genista complex and the Lupinus clade (Fig. 1). The SA spp. of Argyrolobium formed a fully supported subclade. Consistent with ITS and rbcL datasets, A. uniflorum and A. roseum were sister to Dichilus + Melolobium, while A. zanonii was close to members of Cytisus–Genista complex.
Combined ITS + rbcL phylogeny of tribe Genisteae. Argyrolobium + Anarthrophyllum group, Cytisus–Genista complex and Lupinus clades are indicated to the right. Bootstrap percentage (BP >50%) and Bayesian posterior probabilities (PP ≥0.90) are indicated above and below the branch respectively.
Figure 1 Long description
The phylogenetic tree displays the relationships within the Genisteae tribe, organized horizontally from left to right. The tree is divided into three main clades: Lupinus clade, Anarthrophyllum plus Argyrolobium group and Cytisus–Genista complex. The Lupinus clade includes L. argenteus, L. bicolor and L. concinnus. The Anarthrophyllum plus Argyrolobium group is highlighted with different colors for subgroups: Argyrolobium, Sellocharis, Anarthrophyllum and Polhillia. Argyrolobium includes A. harveyanum, A. marginatum, A. molle, A. pachyphyllum and A. paradoxum. Sellocharis and Anarthrophyllum include A. andicola. Polhillia includes P. brevicalyx, P. obsoleta and P. involucrata. The Melolobium subgroup includes M. obcordatum, M. canescens, M. exudans, M. adenodes, M. candicans, M. humile and M. microphyllum. Dichilus includes D. gracilis, D. strictus, A. uniflorum and A. roseum. The Cytisus–Genista complex includes A. zanonii, C. scoparius and L. nigricans. Bootstrap percentages and Bayesian posterior probabilities are indicated above and below the branches, respectively, with values above 50 percent and 0.90 highlighted. The scale bar at the bottom represents genetic distance.
Earlier molecular analyses hinted that Argyrolobium might not be monophyletic (Käss and Wink Reference Käss and Wink1997; Kajita et al. Reference Kajita, Ohashi, Tateishi, Bailey and Doyle2001; Ainouche et al. Reference Ainouche, Bayer, Cubas and Misset2003). Consistent with these findings, the present results recovered A. zanonii (Mediterranean–North African species), outside the SA Argyrolobium clade, aligning with Cytisus–Genista complex, while A. uniflorum (Mediterranean–North African–Southwest Asian species) formed affinities with Melolobium + Dichilus clade. Crucially, A. roseum was also placed close to Melolobium + Dichilus distinct from A. zanonii and the SA assemblage in all analysis. Although based on limited taxon sampling and currently available molecular data, these preliminary results indicate that A. roseum may represent a distinct lineage relative to African and Mediterranean congeners.
Historically, Argyrolobium has been treated as a morphologically cohesive genus distributed across Africa, Mediterranean and Asia. However, pronounced regional morphological differences have long been recognized. The SA spp. are mostly ascending herbs, subshrubs/shrubs, often woody or suffrutescent at base, with persistent, broad-based stipules that are linear to foliaceous, occasionally connate and a dense sericeous/tomentose indumentum on the leaves, calyces and fruits. Their inflorescences are elongate, many-flowered, often with large, bilabiate and sometimes dimorphic flowers. In contrast, the non-SA representatives of the genus are mostly prostrate or decumbent herbs, exstipulate or with minute subulate stipules with glabrous or sparsely pilose foliage and few-flowered or solitary inflorescences. Their flowers are smaller, non-dimorphic and less pubescent, with pods that are shorter and contain fewer seeds (Table 1). These consistent morphological differences in stipules, indumentum and inflorescence suggest morphological divergence between SA and non-SA Argyrolobium species, supporting the phylogenetic divergence uncovered in this study.
A. roseum is morphologically distinct from Mediterranean and African taxa, differing particularly in its prostrate herbaceous habit, glabrous upper leaf surface, few-flowered leaf-opposed racemes and uniquely variable corolla colours (Table 1). These characters, together with presented molecular evidence, support possible evolutionary divergence from SA and Mediterranean congeners.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S1479262126100732
Funding statement
Funds were provided by Department of Biotechnology, Govt. of India, Ministry of Science and Technology vide file no. BT/INF/22/SP41297/2021 (DBT BUILDER) and Bharati Vidyapeeth (Deemed to be) University.
Competing interests
The author declares none.
