Background and aims – A previously undescribed species of Medicago was discovered in Belgium. Its identification and characterization are important for understanding non-native plant introductions linked to historical human activities.

Material and methods – Morphological traits of the single individual found were assessed and compared with related species. Phylogenetic analyses were conducted using nuclear ITS and GA3ox1 markers, as well as plastid matK sequences, to establish genetic relationships.

Key results – Medicago peregrina sp. nov. displays a unique combination of morphological features distinguishing it from other Medicago species. Phylogenetic evidence supports its status as a novel taxon. The species was found on a disturbed riverbank of the Vesdre River in Goffontaine, Belgium, following a major flood in 2021. The species is clearly non-native to the region and is likely associated with historical wool processing activities in the valley. Genetic affinities and the origins of imported wool suggest its native range lies in the Middle East and adjacent regions, although it has not yet been documented there.

Conclusion – The discovery of Medicago peregrina sp. nov. illustrates how historical trade can leave transient botanical traces and highlights the value of continued botanical surveys in disturbed habitats. This case emphasizes the need to consider historical human activity when interpreting the presence of non-native plants.

alien species, Leguminosae, Middle East, phylogenetics, plant taxonomy, Vesdre River, wool industry

The traditional delimitation of the genus Medicago L. underwent significant revision several decades ago, when species of Trigonella L. that shared the characteristic tripping mechanism of the flowers with Medicago – the so-called “medicagoid Trigonella” – were transferred to Medicago (Small 1987; Small et al. 1987; Small and Jomphe 1989; Bena 2001). This reclassification substantially increased the number of recognized species within the genus. In its current circumscription, the genus comprises 91 species and hybrids, predominantly distributed across temperate and subtropical regions of Eurasia and the Mediterranean (POWO 2025).

Medicago includes species of considerable economic importance, most notably the forage crop alfalfa (M. sativa L.), and has therefore been the focus of extensive research across a wide range of disciplines, including molecular phylogenetics (Bena 2001; Chen et al. 2021). A comprehensive global monograph of the genus was published relatively recently (Small 2011), yet new taxa continue to be described. The most recent example is M. tetraprostrata J.S.Erikss. & B.E.Pfeil, a cryptic species believed to result from hybridization between M. prostrata Jacq. and M. sativa (Eriksson et al. 2017).

Over the past few decades, an unexpectedly large number of new Medicago species have been described, the majority of which originate from the Middle East – widely recognized as the primary centre of diversity for the annual taxa within the genus (Small 2011). These include M. syriaca E.Small, native to Syria and southwestern Iran (Small 1990a); M. rigiduloides E.Small, ranging from the eastern Mediterranean to Central Asia (Small 1990b); M. heldreichii E.Small and M. huberi E.Small from southwestern Turkey (Small et al. 1987); M. laxispira Heyn from Iraq; M. makranica Heyn from Pakistan (Heyn 1984); and M. hypogaea E.Small, which occurs from the eastern Mediterranean to Iraq (Small and Brookes 1984). While this concentration of recent discoveries is consistent with the region’s status as a biodiversity hotspot for the genus, it also underscores how incompletely Medicago has been studied in its core range. Notably, molecular data remain unavailable for many of these species, limiting our ability to rigorously test morphology-based species delimitations and to assess their phylogenetic placement and biogeographic origins with confidence.

The presence of spiny fruits in many Medicago species has facilitated their unintentional spread as weeds across much of the world, primarily through epizoochorous dispersal. In particular, the fruits readily attach to animal skins – most notably the fleece of sheep and other wool-bearing animals – allowing species to be inadvertently transported over long distances to regions outside the genus’ native range, such as Australia, South Africa, and South America. As a result, species like M. polymorpha L. have become naturalized in many parts of the world. Medicago species are among the most characteristic so-called “wool aliens”, a term used for alien plants introduced via contaminated wool. In Australia, for instance, they are considered some of the most common and troublesome contaminants in raw wool, posing significant challenges for processing (Australian Wool Testing Authority 1986). In addition to the morphological adaptations that enhance dispersal, Medicago seeds are water-impermeable (“hard seeds”), a trait that enables them to persist in the soil seed bank for extended periods – often decades, or even over a century – without losing viability (Small 2011).

In eastern Belgium, the valley of the Vesdre River, particularly around the town of Verviers, was historically a major centre of the wool processing industry. For over a century, raw wool was imported from distant regions, primarily from the Southern Hemisphere (notably Australia, South Africa, and South America), but also from the Middle East and North Africa (Visé 1942, 1958). During processing, the wool was washed in local facilities, and the wastewater – containing dirt, as well as fruits and seeds – was discharged into the river. Downstream of the factories, under favourable conditions (especially during hot, dry summers), many alien plant species germinated. In this way, exotic species were introduced continuously into the local flora for more than a century. This phenomenon of wool-mediated plant introduction has received considerable attention in other parts of Europe as well (e.g. Hayward and Druce 1919; Probst 1949; Lousley 1961; Ryves 1974). However, from the late 1960s onwards, the direct discharge of untreated wastewater into the river ceased for environmental reasons, and the wool alien flora gradually disappeared.

In July 2021, the Vesdre Valley was severely affected by catastrophic flooding, which caused widespread destruction throughout the region. As a consequence, sediments along the riverbanks were displaced, exposing buried seeds that had remained dormant for decades. In the summer of 2022, a remarkably rich and diverse adventive flora emerged on the newly disturbed alluvial soils. This flora was composed predominantly of species from the regions that historically supplied raw wool – Australia, South Africa, and South America – but also included taxa from North Africa, the Middle East, and the Indian subcontinent (Verloove et al. 2023, in press). In addition to widespread cosmopolitan weeds, several rare and endemic species were encountered, some with remarkably restricted native ranges. Notably, several taxa had not even been formally described at the time of their introduction, including, for example, Sida sivarajanii Tambde, Sardesai & A.K.Pandey, a species recently described from India (Tambde et al. 2020).

Among the species that emerged following the 2021 floods was a taxon of Medicago previously unknown to science. Extensive comparison with all morphologically similar and phylogenetically related Medicago species, based on the most recent global monograph (Small 2011) and publicly available molecular data, revealed no match. The Vesdre specimen is thus recognized as a species new to science. Its discovery highlights the value of combining molecular and morphological evidence to document previously unrecorded diversity.

To evaluate the identity of the Vesdre specimen, we compared it to all currently recognized Medicago species, including recently described and geographically restricted taxa. No previously described species matched, confirming that this is a species new to science.

Molecular phylogeny

Our phylogenetic analyses based on nuclear ITS and GA3ox1, as well as plastid matK sequences indicated that the specimen collected from the Vesdre River represents a distinct lineage, clearly divergent from all publicly available sequences of previously described Medicago species (Fig. 1). Due to differences in taxon sampling across the three markers, determining the specimen’s closest relative(s) remains challenging. GA3ox and matK suggest a phylogenetic affinity with M. heyniana Greuter, while ITS supports a broader relationship with M. polymorpha, M. sativa, and allied species.

Figure 1. 

Maximum likelihood trees (IQ-TREE) inferred from the ITS, GA3ox, and matK sequence alignments, showing the position of Medicago peregrina in bold. Values at branches correspond to UFBoot2 supports (1000 replicates). Scale represents estimated substitutions per site.

Taxonomic treatment

Medicago peregrina Verloove & Gonggrijp, sp. nov.

urn:lsid:ipni.org:names:77375896-1

Figs 2, 3, 4

Type

BELGIUM – Province of Liège • Goffontaine (Pepinster), River Vesdre; 50°33.88’N, 5°45.66’E; 25 Aug. 2022; Verloove F. 14585; gravelly area next to the river; a single specimen; holotype: BR [BR0000027058572V]; cultivated specimens grown from seed of the holotype will be deposited at P and K herbaria.

Figure 2. 

Medicago peregrina. A. Habit. B. Lower leaflet surface, showing detail of indumentum. C. Upper leaflet surface. D. Variation in stipule shape. E. Basal (upper) and apical view of fruit. F. Seed. G. Lateral view of fruit, showing number of coils. A–G from Verloove 14585 (BR0000027058572V). Drawn by Sven Bellanger.

Diagnosis

Genetically most closely related to Medicago heyniana but readily distinguished by its smooth seeds (vs rugose), smaller, hairy, blackening fruits with only two coils (vs larger, glabrous, yellow-greenish fruits with 2.5–4.5 coils), (sub)entire stipules (vs toothed), and an indumentum composed of simple, papillose hairs (vs simple, non-papillose hairs).

Figure 3. 

Medicago peregrina in the field in Goffontaine, Belgium on 25 August 2022. Stems are moderately to densely hairy; leaflets have entire margins and are folded upwards; fruits typically develop only one or two coils. Photo by Rutger Barendse.

Description

Annual herb, branched from the base; branches up to 28 cm long, prostrate to ascending, not rooting at the nodes; indumentum sparse to moderately dense, composed of subappressed to erect, simple, papillose hairs. Leaves trifoliolate; leaflets often folded along the midvein, which is sunken and conspicuous; leaflets ca 5 × 3 mm, obovate, with entire margins, apex retuse to emarginate and mucronulate; upper surface glabrous, lower surface hairy, especially along midrib. Stipules triangular, entire to very shallowly toothed at the base. Inflorescence consisting of a single flower, initially nearly sessile in the leaf axils; peduncle later elongating slightly, up to 6 mm long, always shorter than the subtending petiole; peduncle not aristate, but bearing a small bract ca 1 mm long, inserted 1–1.5 mm below the flower. Flowers small, ca 4.5 mm long, bright yellow. Standard ca 3 mm long, clearly exceeding the wings and keels; abaxial side suffused with pink near the apex. Wings and keels equal, ca 2 mm long. Anthers minute, 0.1–0.15 mm long. Calyx ca 3 mm long, sparsely pubescent; teeth narrowly triangular, about as long as the tube. Fruit ca 6 mm in diameter, uniformly pubescent with simple, papillose hairs; composed of two loosely appressed, flattish coils with soft walls (the second coil typically slightly smaller); coil face bearing ca 8 veins originating from the ventral suture and curving concentrically, with anastomoses before entering the lateral vein. Dorsal suture armed with two rows of slender, flexible, straight spines, widened and grooved at the base, and 2-rooted; spines ca (0.5–)1–1.5 mm long, inserted almost parallel to slightly oblique to the coil face. Seeds 4–6 per coil, not separated by septa; smooth, yellowish brown, ca 1.7 × 1.1 mm.

Figure 4. 

A. Young fruit of Medicago peregrina. The fruit is uniformly pubescent and armed with two rows of slender, straight spines, inserted almost parallel or slightly oblique to the coil face. B. Mature fruit of M. peregrina. The fruit turns blackish at maturity. C. Seed of M. peregrina. In contrast to M. heyniana, the seed has a smooth surface. D. Close-up of the indumentum on the fruit surface of M. peregrina. Hairs are remarkably papillose, a rather rare feature in the genus. E. SEM image (×430) of papillose hairs of M. peregrina. F. SEM image (×850) of a papillose hair of M. peregrina.

Origin

The native range of Medicago peregrina can only be hypothesized. However, by considering both the provenance of the imported wool and the inferred phylogenetic affinity of the species, its potential area of origin can be reasonably narrowed. Among the primary wool-exporting regions – Australia, South Africa, and South America – no native Medicago species are known to occur. These areas only host a limited number of widespread, cosmopolitan species that have become naturalized.

By contrast, the genus Medicago has its primary centre of diversity in the Caucasus, northwestern Iran, and northeastern Turkey (Badri and Ludidi 2023). Notably, several of the more recently described species of Medicago are native or even endemic to this region. The closest known genetic relative of M. peregrina is M. heyniana, a rare and narrowly distributed species confined to the eastern Mediterranean. Considering that a portion of the wool imported into the Vesdre Valley originated from the Middle East – as also evidenced by the presence of other wool aliens such as Trigonella caelesyriaca Boiss., native to parts of the Levant subregion of the Middle East – this area emerges as the most plausible native range of the newly described species.

Further support for this hypothesis comes from molecular evidence. The nuclear internal transcribed spacer (ITS) sequences place M. peregrina within a clade that includes both widely distributed species – such as M. sativa and M. polymorpha – and taxa with more geographically restricted ranges centred on the Middle East, the Caucasus, and adjacent regions. These include: M. constricta Durieu (eastern Mediterranean to Iran; all ITS sequences from Iran), M. daghestanica Rupr. ex Boiss. (Caucasus; sequence from the Northern Caucasus in Russia), M. lessingii Fisch. & C.A.Mey. ex Kar. (eastern Europe to western Siberia and Iran; sequence from Israel), M. rigiduloides (eastern Mediterranean to Central Asia; sequences from Iran), M. saxatilis M.Bieb. (southern Ukraine, Crimean Peninsula), and M. sinskiae Uljanova (northeastern Iran to southern Turkmenistan; sequences from Iran).

Additionally, sequences from more widespread species within the same clade – such as M. rigidula (L.) All. (GenBank accession numbers KX027582, KX027589) and M. polymorpha (MZ356153, OK036668) – also originate from Iran. This geographic clustering provides compelling evidence that the clade, and likely also M. peregrina, originated in the region encompassing Iran and adjacent territories, while acknowledging that some related taxa extend into the Caucasus and adjacent parts of eastern Europe.

Ecology

Since Medicago peregrina was introduced as a contaminant in sheep wool, it is inferred that the species originally inhabited natural pastures historically grazed by sheep in its area of origin. This suggests that its ecological niche is similar to that of other species associated with traditional grazing lands.

Etymology

The specific epithet peregrina – the feminine gender form that agrees with the gender of the generic name Medicago (see ICN Articles 23.5 and 62; Turland et al. 2025) – is derived from the Latin adjective peregrinus (masculine – peregrinus, feminine – peregrina, neuter – peregrinum), meaning “foreigner”, “stranger”, “pilgrim”, or “temporary resident”. It alludes to the species’ uncertain provenance and its presumed introduction far from its native range. The epithet also evokes a broader historical context: it has previously been applied to some alien plant species of unknown origin introduced through wool imports, so-called “wool aliens”. A notable example is Lepidium peregrinum Thell., described from the British Isles by Thellung (1913) and only later identified as native to Australia.

Preliminary IUCN conservation assessment

The conservation status of Medicago peregrina is currently assessed as Data Deficient (DD) according to the IUCN Red List criteria. The species’ natural distribution, habitat preferences, and the number and size of its populations remain unknown. However, several considerations suggest that it may be rare, and possibly even extinct in parts of its potential native range.

Firstly, given the species’ introduction as a wool contaminant, it is hypothesized that M. peregrina is native to the grasslands of Iran, where largescale sheep breeding for wool production has occurred since the 19^th century. Overgrazing is a well-known threat to native flora in such pastoral systems. For example, Acacia loderi Maiden and Senna aciphylla (Benth. ex A.Gray) Randell, both native to Australia and recently also recorded as wool aliens along the Vesdre River (Verloove et al. in press), have experienced substantial population declines in their native range due to grazing pressure (Auld et al. 2015).

Secondly, significant taxonomic research has been conducted on the genus Medicago in Iran, including extensive herbarium studies (Mehregan et al. 2002), as well as detailed cytological and molecular phylogenetic work (e.g. Ghanavati et al. 2007; Ghanavati 2011; Sadeghian et al. 2014; Zareei et al. 2020; Bayat et al. 2021; Zareei et al. 2022). These investigations indicate that Medicago species are relatively well documented in surveyed parts of the country. Unless M. peregrina originates from an unsampled region of Iran, it is reasonable to suggest that it may indeed be very scarce (if not extinct) in known areas – although, given Iran’s very large size (~1.65 million km²), it could still persist in poorly explored regions.

Finally, targeted field surveys throughout Iran are needed to clarify the species’ true distribution and conservation status.

Observations

Belgium, Goffontaine (Pepinster), River Vesdre, 50°33.88’N, 5°45.66’E, 25 Aug. 2022, obs. by Filip Verloove, Sipke Gonggrijp, and Rutger Barendse, https://waarnemingen.be/observation/253272516/, https://waarnemingen.be/observation/253400528/, https://waarnemingen.be/observation/253566416/.

Notes

The new species does not closely resemble any previously described taxon. According to the provisional infrageneric classification proposed by Small (2011), it belongs to Medicago sect. Spirocarpos Ser., subsection Spirocarpos, a morphologically heterogeneous and weakly supported group, often regarded as a “dust bin” taxon. Although its placement within this subsection is based on general fruit morphology, the new species exhibits several uncommon features, including an indumentum of papillose hairs.

Phylogenetic analyses based on both plastid (matK) and nuclear (GA3ox1) markers consistently place M. peregrina in a clade closely related to M. heyniana, a rare and geographically restricted species currently considered the sole member of the monotypic sect. Heynianae Greuter. Medicago heyniana was originally described from the island of Karpathos in the eastern Aegean (Greuter 1970) and has since been reported from several other Greek islands (e.g. Amorgos, Anafi, Rhodos) and southwestern Turkey (Lassen 1983; Özhatay et al. 1999; Thanopoulos 2007; Kougioumoutzis et al. 2012).

Medicago peregrina is distinct both at the molecular and morphological level, representing a lineage separate from all previously described Medicago species.

Medicago peregrina is a genetically and morphologically well-defined species, clearly distinct from all closely related Medicago taxa. Although its precise native range remains unknown, molecular affinities, biogeographic patterns within Medicago, and the historical origins of wool imported into the Vesdre Valley collectively point to the Middle East and adjacent regions as the most plausible source area.

This study demonstrates the value of integrating molecular and morphological evidence when assessing the identity of rare or previously unrecognized taxa introduced outside their native range. The discovery of M. peregrina also underscores the importance of broader sampling –in particular in the Middle East – to better resolve the species’ distribution, genetic diversity, and conservation status.

We would like to thank the following persons, all affiliated with Meise Botanic Garden, Belgium: Sven Bellanger for the original line drawings, Iris Van der Beeten for the photographs, and Liliane Tytens for preparing the photographic plate; our gratitude also goes to Ann Van de Vyver for the ex situ cultivation work, and to Wim Baert and Arne Mertens for their assistance in the molecular laboratory. In addition, we thank Rutger Barendse (Genk, Belgium) for kindly providing the field photograph used in this study. We sincerely thank the editors and all three reviewers for their careful reading of the manuscript and for their constructive comments and suggestions, which have greatly improved the clarity and quality of the paper.