Lappula monocarpa is currently the sole described species within the genus Lappula characterized by the development of a single nutlet per fruit. However, since its initial publication, no additional specimens of L. monocarpa have been collected. Critical examination of type specimens, combined with field surveys and newly collected material, reveals that the diagnostic trait of L. monocarpa—the presence of a single nutlet per fruit—is not consistently observed and likely represents an aberrant specimen. Moreover, all other morphological characteristics of L. monocarpa, including indumentum, corolla, and nutlet features, align fully with those of L. tenuis. Based on this evidence, L. monocarpa is herein reduced to a synonym of L. tenuis.

Boraginaceae, Lappula, morphology, new synonym

Lappula Moench is one of the largest genera within the tribe Rochelieae of the family Boraginaceae (Chacón et al. 2016; Vasile et al. 2025). It comprises approximately 50 to 80 species distributed across Eurasia, North Africa, North and South America, and Australia, with a center of diversity located in Central Asia (Wang 1981; Ovczinnikova 2005, 2021; Weigend et al. 2016). Members of Lappula are characterized by blue or white corollas with five throat appendages, a subulate gynobase, and heteromorphic or homomorphic nutlets bearing marginal glochids or wings (Popov 1953; Riedl 1967; Wang 1981; Ovczinnikova 2005). In China, 36 species of Lappula have been recorded (Zhu et al. 1995), of which at least nine are endemic.

Lappula monocarpa C.J.Wang is a Chinese endemic species, restricted to Xinjiang Province (Wang 1981). It was originally described based on a specimen collected from Heishantou (Black Mountain), Jimunai County, Xinjiang. The species is distinguished by the production of a single, horizontally oriented nutlet per fruit, with a disc margin bearing a single row of glochids. In the protologue, Wang (1981) emphasized that these morphological traits are highly distinctive within Lappula, particularly the presence of a solitary nutlet, which clearly separates L. monocarpa from all other taxa of Lappula. Concurrent with the species description, Wang (1981) also established a new monotypic subsection, Lappula subsect. Monocarpae C.J.Wang, to accommodate it. However, since its original description, no additional specimens of L. monocarpa have been collected beyond the type specimen.

The nutlets of L. monocarpa bear a single row of marginal glochids with non-connate bases. Based on these traits, Ovczinnikova (2005) assigned L. monocarpa to ser. Strictae, a classification that contradicts Wang’s (1981) earlier taxonomic treatment. Subsequently, Ovczinnikova (2009) proposed that L. monocarpa may represent only a variant of L. stricta, distinguished solely by its production of a single nutlet per fruit. Nutlet characteristics are extensively utilized for infrageneric classification and species delineation within Lappula. These characteristics include the presence of glochids or wings, the number of glochid rows, the length of the glochids, the width of the wings, and the shape of the dorsal disk (Gürke 1894; Popov 1953; Riedl 1967; Wang 1981; Ovczinnikova 2005, 2009, 2021). However, the number of nutlets per fruit has not been employed as a diagnostic character for species delineation, as all currently described species of Lappula typically develop four nutlets per fruit, with the exception of L. monocarpa (Popov 1953; Wang 1981; Ovczinnikova 2005, 2021, 2023; Liu et al. 2024).

Further examination of the type specimen of L. monocarpa revealed that it bears only a few developing fruits, each containing a single nutlet. This nutlet is ovoid and features a single row of glochids (Fig. 1). Apart from the difference in nutlet number, all other nutlet characteristics align fully with those of L. tenuis (Ledeb.) Gürke. These observations suggest that L. monocarpa and L. tenuis represent the same taxonomic entity. To test this hypothesis, field surveys were conducted at the type locality of L. monocarpa, and additional specimens were collected. Morphological comparisons among L. monocarpa, L. tenuis, and L. stricta (Ledeb.) Gürke were then carried out to clarify the taxonomic status of L. monocarpa.

Figure 1. 

Type specimen of Lappula monocarpa C.J.Wang. A. Holotype in the herbarium of the Northwest Institute of Plateau Biology, Chinese Academy of Sciences (HNWP); B, C. Details of the holotype; B. Development of a single nutlet per fruit, with the nutlet horizontally oriented; C. Nutlet morphology.

Herbarium specimens of Lappula from ALTB, BNU, HNWP, KUZ, LE, and NSK were thoroughly examined, including the type specimens of L. monocarpa and L. tenuis. A field survey was conducted at the type locality of L. monocarpa in Heishantou (Black Mountain), Jimunai County, Xinjiang Province, China, where additional specimens were collected and deposited at BNU. Detailed morphological features, including stem indumentum, calyx, corolla, nutlets, and gynobase, were documented in situ using a Sony Alpha 7 camera. Comparative morphological analyses of L. monocarpa, L. stricta, and L. tenuis were performed to assess their taxonomic boundaries.

During field investigations, no Lappula specimens matching the original description of producing a single nutlet per fruit were encountered. All collected individuals consistently developed four nutlets per fruit. Aside from this numerical discrepancy, their morphological features were indistinguishable from those described for L. monocarpa. Detailed morphological comparisons among L. monocarpa, L. stricta, and L. tenuis revealed congruent characteristics in stem indumentum, bract morphology, calyx, and corolla (Fig. 2, Table 1). The primary diagnostic differences were confined to nutlet morphology: both L. monocarpa and L. tenuis exhibit ovate dorsal disks (length-to-width ratios of 2.5–3), with the greatest width occurring below the midpoint. These nutlets lack a disk keel and possess non-thickened margins. In contrast, nutlets of L. stricta are lanceolate (length-to-width ratio ~4), may or may not display a disk keel, and typically have thickened margins.

Figure 2. 

Morphological features of Lappula monocarpa C.J.Wang (A–J) and nutlet morphology of L. stricta (Ledeb.) Gürke (K) and L. tenuis (Ledeb.) Gürke (L). A. Characteristics of stem trichomes, showing appressed and spreading hairs; B. Calyx; C, D, E, F. Flower morphology; C, D. Lateral view of the flower; E. Top view of the flower; F. Expanded flower morphology, showing the corolla throat appendages and stamens; G. Gynobase morphology; H, I, J. Nutlet morphology; H. Abaxial view of the nutlet; I. Lateral view of the nutlet; J. Adaxial view of the nutlet; K. Nutlet morphology of L. stricta; L. Nutlet morphology of L. tenuis. Scale bars: 1 mm.

Ovczinnikova (2005) circumscribed Lappula sect. Lappula to include five series: ser. Lappula, ser. Redowskianae Ovczinnikova, ser. Anisacanthae Ovczinnikova, ser. Strictae M.Pop. ex Ovczinnikova, and ser. Patulae Ovczinnikova (Table 2). Recently, Liu et al. (2025) reconstructed the phylogenetic relationships of Asian Lappula using hundreds of single-copy nuclear genes and complete chloroplast genomes. Their results support the monophyly of sect. Lappula as defined by Ovczinnikova (2005). However, the placement of certain taxa conflicts with this classification. Notably, L. monocarpa clustered with L. consanguinea and L. anocarpa, indicating a closer affinity with ser. Lappula. Furthermore, L. monocarpa and L. stricta occupy distinct, strongly supported subclades within sect. Lappula (Clade IV; Liu et al. 2025). This phylogenetic topology supports neither the inclusion of L. monocarpa in ser. Strictae (Ovczinnikova 2005), nor the hypothesis that L. monocarpa represents a variant of L. stricta (Ovczinnikova 2009).

Ovczinnikova (2005) defined ser. Strictae as comprising taxa with nutlets bearing a single row of glochids, typically with broadened bases or, occasionally, forming marginal wings. In contrast, ser. Lappula includes nutlets with one to several rows of glochids, the bases of which are neither broadened nor winged. Ovczinnikova assigned L. monocarpa to ser. Strictae and L. tenuis to ser. Lappula. However, both the type specimen of L. monocarpa and newly collected material from its type locality reveal that the glochids have neither broadened nor winged bases, and no winged nutlets were observed in the population. These morphological traits are inconsistent with the defining characteristics of ser. Strictae.

Detailed morphological comparisons between the Asian Lappula taxa L. stricta (ser. Strictae) and L. tenuis (ser. Lappula) reveal that the primary distinguishing feature between these two series lies in the shape of the nutlet disk, rather than in the number of glochid rows. The “disk” refers to the flattened area on the dorsal side of the nutlet, the margin of which typically bears glochids or wings (Hilger 2014). Nutlets of ser. Strictae are lanceolate and may or may not possess a keel, whereas those of ser. Lappula are ovate and consistently keel-less. The nutlet disk of L. monocarpa is ovate and lacks a keel, supporting its placement within ser. Lappula on morphological grounds, in agreement with the phylogenetic results of Liu et al. (2025). Additionally, some North American Lappula taxa, such as L. desertorum Greene and L. heterosperma Greene, exhibit a ridge on the dorsal face of the nutlet or lines of tubercles along the midline of the disk (Rolfsmeier 2013). Liu et al. (2025) suggested that these North American taxa may be closely related to Clade IV on the Eurasian continent. The species examined in the present study, L. monocarpa and L. stricta, also belong to Clade IV. While sect. Lappula, as defined by Ovczinnikova (2005), includes only one native North American species, L. occidentalis (S. Watson) Greene, the phylogenetic placement of other North American Lappula taxa remains uncertain and requires further investigation using both molecular and morphological data.

As defined by Ovczinnikova (2005), ser. Lappula comprises seven species, among which only L. tenuis and L. brachycentroides Popov produce nutlets with a single row of spines. Popov (1951) noted that L. brachycentroides is closely related to Echinospermum tenue Ledeb. (now accepted as L. tenuis), differing primarily by the presence of short or absent glochids on the nutlets. The nutlets of L. monocarpa bear a single row of glochids with non-broadened bases and exhibit an ovate, non-lanceolate dorsal disk. Taken together, the molecular phylogenetic findings of Liu et al. (2025) and the morphological evidence presented here support the placement of L. monocarpa within ser. Lappula. This classification supports the reduction of L. monocarpa to a taxonomic synonym of L. tenuis.

The author expresses sincere gratitude to the curators of the herbaria ALTB, BNU, HNWP, KUZ, LE, and NSK for providing access to specimens and digital images for examination. Appreciation is also extended to the anonymous reviewer for their valuable and constructive comments, which substantially improved the quality of the manuscript.