An interesting conundrum was recently revealed by R. Abbott when he found that the number of hybrid zones reported in the literature for plants is very low, given the propensity of plants to hybridise. In another literature survey on hybrid zones performed over the period 1970–2022, we found that the number of hybrid zones reported for vertebrates was 2.3 times greater than that reported for vascular plants, even though there are about six times more vascular plant species than vertebrates. Looking at the number of papers reporting hybrid zones, there are 4.9 times more on vertebrates than on vascular plants. These figures support the relevance of this conundrum. In this paper we aim to shed light on this question by providing a structured discussion of the causes that may underlie this conundrum. We propose six non-mutually exclusive factors, namely lack or deficit of spatial structure, lack or deficit of genetic structure, effects of hybridisation between non-closely related species, lability of plant hybrid zones over time, botanists’ perception of hybridisation, and deficit of population genetic data. There does not appear to be a single factor that explains our puzzle, which applies to all cases of plants where hybridisation is detected but no hybrid zone is reported. It is argued that some plant features suggest that the puzzle is not, at least entirely, due to insufficient knowledge of the specific cases, a hypothesis that should be addressed with a wider range of empirical data across different taxonomic groups.

R. Abbott 最近发现了一个有趣的难题，他发现考虑到植物的杂交倾向，文献中报道的植物杂交区的数量非常低。在另一项关于 1970 年至 2022 年期间进行的混合区文献调查中，我们发现，报告的脊椎动物混合区数量是维管植物报告的 2.3 倍，尽管维管植物种类比脊椎动物多约六倍。从报告杂交区的论文数量来看，脊椎动物的论文数量是维管植物的 4.9 倍。这些数字支持了这个难题的相关性。在本文中，我们旨在通过对可能构成这一难题的原因进行结构化讨论来阐明这个问题。我们提出了六个非互斥因素，即空间结构的缺乏或缺陷、遗传结构的缺乏或缺陷、非密切相关物种之间杂交的影响、植物杂交区随时间的不稳定性、植物学家对杂交的看法以及缺陷群体遗传数据。似乎没有一个因素可以解释我们的难题，这适用于检测到杂交但没有报告杂交区的所有植物情况。有人认为，一些植物特征表明，这个难题至少不是完全由于对具体情况的了解不足而造成的，这一假设应该通过不同分类群的更广泛的经验数据来解决。