Lejeunea (sect. Minutilobae) R. M. Schust.

[Clade XV]Lejeunea sect. MinutilobaeR. M. Schust. (Schuster 1980: 1031) Byssolejeunea Herzog (Herzog 1941: 84) – Type species: Lejeunea abnormis Herzog (= L. exilis var. abnormis (Herzog) G. E. Lee). Cardiolejeunea R. M. Schust. & Kachroo (Schuster 1963: 149) – Type species: C. cardiantha R. M. Schust. & Kachroo (= L. papilionacea Prantl). Stenolejeunea R. M. Schust. (Schuster 1963: 144) – Type species: S. thallophora (Eifrig) R. M. Schust. (= L. thallophora (Eifrig) Gradst.). Type species Lejeunea minutiloba A. Evans. Description Plants delicate, mostly less than 1 mm wide. Stem epidermis cells only slightly larger than medullary cells, rarely bulging outwards, medullary cells few, in 5–12 (– 15) rows. Cuticle smooth or finely punctate-papillose. Oil bodies usually granular, rarely homogeneous (L. dimorpha, L. minutiloba). Male bracteoles restricted to the base of the male spike. Innovations present, sterile or fertile but not repeatedly fertile. Perianth 5 - keeled (eplicate in L. exilis var. exilis), keels smooth to frequently crenate by mammillose cells or toothed, lateral keels sometimes expanded as auricles (L. papilionacea). Asexual reproduction by strap-shaped gemmae in Asian-Australasian members of the section, rarely by cladia (L. dimorpha). Distribution Pantropical. Species Lejeunea adpressa Nees, L. anisophylla Mont., L. apiculata Sande Lac., L. compressiuscula (Steph.) G. E. Lee & Heinrichs, L. dimorpha T. Kodama, L. dipterocarpa E. W. Jones, L. discreta Lindenb., L. exilis (Reinw., Blume & Nees) Grolle, L. heinrichsii G. E. Lee, Bechteler, Pócs & Schäf. - Verw., L. ibadana A. J. Harr. & E. W. Jones, L. malaysiana G. E. Lee & Pócs, L. micholitzii Mizut., L. minutiloba A. Evans, L. papilionacea, L. patriciae Schäf. - Verw., L. subolivacea Mizut., L. tasmanica Gottsche (?), L. thallophora. Further species (not sequenced) Lejeunea morobensis (Grolle) M. A. M. Renner & Pócs. Notes This large section stands out by small plant size, frequency of autoicy (e. g. in a large, robust subclade consisting of L. subolivacea, L. adpressa, L. dipterocarpa, L. papilionacea, L. anisophylla, L. ibadana, L. heinrichsii, L. minutiloba, and L. compressiuscula), thin stems with few medullary cell rows, presence of innovations but absence of repeatedly fertile ones, and the frequency of strap-shaped-gemmae, e. g. in L. exilis, L. malaysiana, and some members of the former genus Stenolejeunea, including L. apiculata, L. morobensis, and L. thallophora. Interestingly, Stenolejeunea schiffneri (Herzog) Pócs (= L. pulchriflora) was found to be a member of sect. Lamacerinae (subg. Lejeunea). The latter section shares numerous characters with sect. Microlobae but differs in 2 - winged perianth keels and predominantly neotropical distribution. The morphological similarity of sect. Lamacerinae and sect. Microlobae exemplifies the strong parallel evolution within Lejeunea. Lejeunea tasmanica has been considered a synonym of L. drummondii (Renner 2013). However, in this study L. drummondii was resolved in the sect. Lejeunea clade highly distant from L. tasmanica. The latter is therefore retained here as a separate species pending further work on the relationship of these two Australian taxa. Several species complexes, potentially comprising multiple independent entities, are identified within the section, including the paleotropical L. papilionacea and the pantropical L. adpressa, which is morphologically similar to L. anisophylla (Gradstein 2021) but occupies a separate lineage in the phylogenetic tree. In view of the molecular results, L. anisophylla and L. adpressa are retained as separate species (despite the lack of discriminating morphological characters) pending further study. References Wigginton (2004), Reiner-Drehwald (2009), Lee (2013), Lee et al. (2019, 2022).