Comparison of the micromorphology of greyish oak (Quercus robur L. subsp. pedunculiflora (K. Koch) Menitsky) and pedunculate oak (Quercus robur L. subsp. robur) inflorescences
Abstract
In the present study, we compared the micromorphology of the inflorescences of greyish oak (Quercus robur L. subsp. pedunculiflora (K. Koch) Menitsky) and pedunculate oak (Quercus robur L. subsp. robur). Greyish oak samples were collected in Romania, while pedunculate oak samples were collected in Hungary and Romania during the springs of 2023, 2024, and 2025, across a total of 11 sites. The 70 samples originated from 33 trees. Micromorphological traits of the inflorescences – primarily the presence and type of trichomes – were examined using scanning electron microscopy (SEM) on the inflorescence axis as well as on floral organs, including cupule primordia, stigma, staminal filaments, and anthers. On both female and male inflorescence axes, trichome density was determined and trichome ray length was measured. Pollen grains were also examined to a limited extent. No indumentum was detected on the stigma, anthers, or staminal filaments in either taxon. In contrast, stellate and fasciculate trichomes were observed on the female inflorescence axis, on cupule primordia, and on the male inflorescence axis in both taxa. In the pedunculate oak samples, some female inflorescences displayed a completely glabrous axis – representing a clear micromorphological distinction between the two taxa in our material. The female inflorescence axis of greyish oak was characterized by approximately fourfold higher trichome density compared to that of pedunculate oak (93.71 vs. 25.00 trichomes/mm²). Longer trichome rays were also recorded in greyish oak, both in stellate trichomes (329.14 ± 86.01 μm) and fasciculate trichomes (468.39 ± 117.31 μm), whereas in pedunculate oak the respective values were 152.63 ± 63.83 μm and 225.59 ± 74.23 μm. A significant difference in pollen grain length was also detected, with values of 35.67 ± 4.11 μm in greyish oak and 32.83 ± 4.04 μm in pedunculate oak. The higher trichome density of greyish oak inflorescences may serve as a useful diagnostic trait in identifying the taxon. A more developed indumentum covering not only the reproductive parts but also the leaves shown in our earlier study may contribute to an improved drought tolerance, a potentially advantageous feature under the recent climate change. This study provides the first detailed micromorphological comparison of the inflorescences of greyish oak and pedunculate oak, thereby contributing new insights into the morphological differentiation of these two closely related taxa.
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