ABSTRACT

Introduction.

The extent and causes of variation in sporophyte production among British dioicous liverworts are assessed.

Methods.

Reproductive attributes of dioicous species are taken from Paton’s The Liverwort Flora of the British Isles (1999 Paton JA. 1999. The liverwort flora of the British Isles. Colchester: Harley Books. [Google Scholar]). The extent to which sporophyte production is potentially restricted by low levels of sex expression, unbalanced phenotypic sex ratios, and probable spatial segregation of the sexes, is quantified. Patterns of variation in sexual reproduction are also characterised for species associated with different biogeographical zones in Europe.

Results.

Of the 188 British liverwort species that are dioicous (62%), sporophytes are unknown in 65, rare in 58, occasional in 50 and frequent in 15. Some species are not or rarely sexually reproductive, but major causes of restricted sexual reproduction are sexual imbalance and probable isolation of the sexes. Among species with skewed sex ratios, female bias is substantially more common than male bias. Sporophyte frequency is relatively high among species widely distributed in temperate and boreal Europe, compared with taxa associated with other climatic zones, including the oceanic fringe.

Conclusions.

Restricted sporophyte production implies that asexual reproduction and clonal longevity are critical for the persistence of many liverworts. Further insights will require field surveys of patterns of sex expression and sporophyte distribution, together with information on reproductive plasticity, genotypic sex ratios, and levels of genetic diversity and structure.

中文翻译：

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英国雌雄异株地草中的孢子体频率

摘要

介绍。

评估了英国双子地艾中孢子体产生变异的程度和原因。

方法。

雌雄异株的繁殖属性取自佩顿的《不列颠群岛的地钱植物群》（1999 年） 佩顿JA。 1999 年。不列颠群岛的地钱植物群。科尔切斯特：哈雷图书。 [谷歌学术]）。量化了孢子体生产受低水平性别表达、不平衡的表型性别比例和可能的性别空间隔离限制的程度。与欧洲不同生物地理区域相关的物种也具有有性生殖变异模式的特征。

结果。

在英国的 188 种地钱属双子植物中 (62%)，65 种孢子体不为人知，58 种罕见，50 种偶见，15 种常见。有些物种不能或很少进行有性繁殖，但有性繁殖受限的主要原因是有性繁殖两性的不平衡和可能的隔离。在性别比例失衡的物种中，雌性偏见比雄性偏见更为普遍。与与其他气候带（包括海洋边缘）相关的分类群相比，广泛分布于温带和北欧的物种中的孢子体频率相对较高。

结论。

受限的孢子体生产意味着无性繁殖和克隆寿命对于许多地钱的持续存在至关重要。进一步的见解将需要对性别表达模式和孢子体分布进行实地调查，以及有关生殖可塑性、基因型性别比例以及遗传多样性和结构水平的信息。