Woodlands in Iceland are characterized by shrub-like birch, a result of introgressive hybridization between diploid dwarf birch, Betula nana, and tetraploid downy birch, B. pubescens. Introgression occurs via triploid hybrids. We evaluated the fertility of triploid birch by examining pollen viability and seed germination. Pollen samples were collected from woodlands throughout Iceland from 99 plants, including 22 triploid hybrids. The germination of pollen from the triploid hybrids was about one third that of the diploid or tetraploid species (mean values: 9% vs. 26% and 29%). Most triploid plants had a pollen germination of less than 2%. However, some showed exceptionally high pollen fertility (six plants: 11–79%). Microscopic examination revealed normal pollen tube growth and elongation in hybrids with low germination, while other hybrids showed abnormal tube growth. Fluorescence microscopy indicated pollen viability in all ploidy groups, with green autofluorescence from the cytoplasmic contents and red fluorescence from the exine wall. The Aniline test of pollen viability showed that grains with three pores (normal, triporate grains) stained positively, but non-triporate grains were unstained and empty. Germination tests were performed on seeds collected from 246 plants, including 21 triploid hybrids. The germination percentage of seeds from triploid hybrid plants was about 20 times lower than that of the diploid or the tetraploid species (population means: 0–4% vs. 3–41% and 6–54%). The present study shows that triploid birch hybrids are not sterile. Both the paternal and maternal fertility of the hybrids should be sufficient to facilitate gene flow via backcrossing with the parental species.

冰岛的林地以灌木状桦树为特征，这是二倍体矮桦桦（Betula nana）和四倍体绒毛桦（B. pubescens）之间渐渗杂交的结果。渗入通过三倍体杂种发生。我们通过检查花粉活力和种子发芽来评估三倍体桦树的繁殖力。从整个冰岛的林地中采集了99株植物的花粉样本，其中包括22种三倍体杂种。来自三倍体杂种的花粉发芽量约为二倍体或四倍体物种的发芽量（平均值：9％比26％和29％）。大多数三倍体植物的花粉萌发少于2％。但是，有些显示出异常高的花粉育性（六种植物：11–79％）。显微镜检查显示，低发芽杂种的花粉管生长和伸长正常，而其他杂种显示花粉管生长异常。荧光显微镜显示所有倍性组的花粉活力，细胞质中的绿色自发荧光，外壁的红色荧光。花粉生存力的苯胺测试表明，具有三个孔（正常，三重谷物）的谷物染色呈阳性，但非三重谷物未染色且为空。对从246种植物（包括21种三倍体杂种）中收集的种子进行了发芽测试。三倍体杂种植物的种子发芽率比二倍体或四倍体物种的发芽率低约20倍（种群数量：0–4％比3–41％和6–54％）。本研究表明三倍体桦木杂种不是无菌的。杂种的父本和母本育性都应足以通过与亲本种回交来促进基因流动。花粉生存力的苯胺测试表明，具有三个孔（正常，三重谷物）的谷物染色呈阳性，但非三重谷物未染色且为空。对从246种植物（包括21种三倍体杂种）中收集的种子进行了发芽测试。三倍体杂种植物的种子发芽率比二倍体或四倍体物种的发芽率低约20倍（种群数量：0–4％比3–41％和6–54％）。本研究表明三倍体桦木杂种不是无菌的。杂种的父本和母本育性都应足以通过与亲本种回交来促进基因流动。花粉生存力的苯胺测试表明，具有三个孔（正常，三重谷物）的谷物染色呈阳性，但非三重谷物未染色且为空。对从246种植物（包括21种三倍体杂种）中收集的种子进行了发芽测试。三倍体杂种植物的种子发芽率比二倍体或四倍体物种的发芽率低约20倍（种群数量：0–4％比3–41％和6–54％）。本研究表明三倍体桦木杂种不是无菌的。杂种的父本和母本育性都应足以通过与亲本种回交来促进基因流动。包括21种三倍体杂种。三倍体杂种植物的种子发芽率比二倍体或四倍体物种的发芽率低约20倍（种群数量：0–4％比3–41％和6–54％）。本研究表明三倍体桦木杂种不是无菌的。杂种的父本和母本育性都应足以通过与亲本种回交来促进基因流动。包括21种三倍体杂种。三倍体杂种植物的种子发芽率比二倍体或四倍体物种的发芽率低约20倍（种群数量：0–4％比3–41％和6–54％）。本研究表明三倍体桦木杂种不是无菌的。杂种的父本和母本育性都应足以通过与亲本种回交来促进基因流动。