Morphology and Viability of Pollen from Three Hardy Water Lilies and Their Cross-Compatibility with <i>Nymphaea hybrid</i>

Owing to the wide variation in their morphological characteristics across diverse geographies, the identification and classification of plants in the <i>Nymphaea</i> genus are challenging. Therefore, the present study investigated the pollen morphological characteristics of hardy water lilies (<i>N.</i> ‘Rose Arey’, <i>N.</i> ‘Perry’s Fire Opal’, and <i>N.</i> ‘Peter Slocum’), their relationship with species classification and system evolution, and their cross-compatibility with three strains of <i>Nymphaea</i><i>hybrid</i> (NH-1, NH-2, and NH-3), a tropical waterlily. Pollen of the hardy water lilies was single-grained, oblate, and 18.31–20.47 × 32.51–37.64 μm. The pollen apertures were of the ring-groove type, and the pollen exine ornamentation was rod- and tumour-shaped. Pollen grains of different species differed in size, the obviousness of tumour ornamentation, and the size and density of rod-like ornamentation; their germination rates also differed significantly. Viabilities of <i>N.</i> ‘Rose Arey’ and <i>N.</i> ‘Peter Slocum’ pollen were the highest and lowest, respectively. According to the artificial pollination results, all hybrid combinations except three (NH-1 × <i>N.</i> ‘Peter Slocum’, NH-2 × <i>N.</i> ‘Peter Slocum’, and NH-3 × <i>N.</i> ‘Peter Slocum’) bore seeds; combinations with NH-2 as the female parent and <i>N.</i> ‘Rose Arey’ as the male parent had the highest seed-setting rates.