Pollen Morphology of Some Galium L. (Rubiaceae) Taxa

This study investigated the palynological characteristics of eleven Galium L. (Rubiaceae) taxa (G. setaceum, G. spurium subsp. spurium, G. aparine, G. rotundifolium, G. odoratum, G. rivale, G. incanum subsp. elatius, G. humifusum, G. verum subsp. verum, G. album subsp. pycnotrichum, and G. paschale) collected from different localities in Eskişehir Province, Türkiye. Pollen grains were examined using scanning electron microscopy (SEM). For each taxon, the polar axis (P), equatorial axis (E), P/E ratio, pollen shape, aperture number, colpus length (Cl), colpus width (Cw), and exine ornamentation were measured. Across the examined taxa, the smallest pollen grains were observed in G. paschale (P = 12.79 µm), whereas the largest were recorded in G. aparine (P = 28.20 µm). The equatorial axis (E) ranged from 8.70 to 19.90 µm, and the P/E ratio ranged from 1.25 to 2.20. Pollen grains were predominantly prolate in G. setaceum, G. spurium subsp. spurium, G. aparine, G. rotundifolium, G. odoratum, G. rivale, G. verum subsp. verum, and G. album subsp. pycnotrichum, whereas G. incanum subsp. elatius, G. humifusum, and G. paschale exhibited subprolate pollen. Aperture numbers ranged from penta- to nonacolpate, and exine ornamentation was consistently microechinate or microechinate–perforate. Although slight quantitative differences were observed among the examined taxa, the extensive overlap in pollen morphological characters indicates that palynological features alone provide limited taxonomic resolution for species-level discrimination within Galium.