Abstract Polyploidization is an important speciation and evolution mechanism in ferns. Initially, new cytotypes face challenges in maintaining themselves within the majority cytotype populations. Unlike in most even-ploidy cytotypes, fern triploids are often apomictic or infertile, due to genetic imbalance. An interesting opportunity to study these phenomena has emerged with the discovery of triploid bracken (Pteridium aquilinum), a triploid fern that is fertile but not apomictic. Originally found in one Welsh population, the distribution of this cytotype in Europe is unknown as is its origin and how it maintains itself among the presumed diploid majority. We sampled 135 populations of P. aquilinum, focusing on Central Europe. Ploidy level of all samples was analyzed by flow cytometry. We compared the two cytotypes via micromorphological characters (spore and stomata size), fertility characteristics (spore abortion and proportion of populations with sporangia-bearing fronds). Additionally, genetic difference between ploidy levels was tested as well. The diploid cytotype of P. aquilinum is dominant in continental Europe with 121 entirely diploid populations found, but we also found 9 mixed and 5 entirely triploid populations. Fertile diploid and triploid plants were found only in 17.7% and 21.4% of populations, respectively. The cytotypes are distinguishable using both tested micromorphological characters, but stomata are more reliable due to overall reduced fertility. Unlike the Welsh specimen, our tested triploid has most spores aborted, ca 97.4%, compared to mean 6.0% of spores aborted in diploids. The triploid cytotype is rare and likely originated multiple times from the diploids and relies on clonal and possibly limited sexual reproduction to maintain itself. However, diploids and triploids are often genetically different within a population, indicating that the triploid may migrate between populations. Due to its vegetative growth and presumed continuous formation, the triploid cytotype is likely to remain established in Central Europe, although in small numbers.

中文翻译：

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欧洲蕨菜 (Pteridium aquilinum) 的细胞型：广泛的二倍体和分散的可能有多种来源的三倍体

摘要 多倍化是蕨类植物重要的物种形成和进化机制。最初，新的细胞类型面临着在大多数细胞类型群体中维持自身的挑战。与大多数偶倍体细胞型不同，蕨类三倍体由于遗传失衡通常是无融合生殖或不育的。随着三倍体蕨菜 (Pteridium aquilinum) 的发现，研究这些现象的一个有趣机会出现了，这是一种可以繁殖但不能无融合生殖的三倍体蕨类植物。最初在一个威尔士人口中发现，这种细胞型在欧洲的分布是未知的，它的起源以及它如何在假定的二倍体多数中维持自身。我们对 135 个 P. aquilinum 种群进行了采样，重点是中欧。通过流式细胞术分析所有样品的倍性水平。我们通过微形态学特征（孢子和气孔大小）、生育特征（孢子流产和带有孢子囊的叶状体的种群比例）比较了两种细胞型。此外，还测试了倍性水平之间的遗传差异。P. aquilinum 的二倍体细胞型在欧洲大陆占主导地位，发现了 121 个完全二倍体种群，但我们也发现了 9 个混合种群和 5 个完全三倍体种群。可育的二倍体和三倍体植物分别仅在 17.7% 和 21.4% 的种群中被发现。使用两种测试的微形态特征可以区分细胞型，但由于整体生育力降低，气孔更可靠。与威尔士标本不同，我们测试的三倍体的大多数孢子中止，约 97.4%，而二倍体中孢子中止的平均比例为 6.0%。三倍体细胞型很罕见，可能多次起源于二倍体，依靠克隆和可能有限的有性繁殖来维持自身。然而，二倍体和三倍体在一个种群内通常在遗传上是不同的，这表明三倍体可能会在种群之间迁移。由于其营养生长和假定的连续形成，三倍体细胞型很可能在中欧仍然存在，尽管数量很少。