The smallest Zosterophyllum plant from the Lower Devonian of South China and the divergent life history strategies in zosterophyllopsids

Plants have evolved different life history strategies to overcome the
limited amount of available resources; however, when and how divergent
strategies of sexual reproduction evolved in early land plants is not well
understood. As one of the notable and vital components of early
terrestrial vegetation, the Zosterophyllopsida and its type
genus Zosterophyllum, reached maximum species diversity during
the Pragian (Early Devonian; ca. 410.8–407.6 million years ago). Here we
describe a new species, Z. baoyangense sp. nov., based on well-preserved
specimens from the Pragian-aged Mangshan Group of Duyun, Guizhou Province,
China. The new plant is characterized by its small size, K-shaped
branching, and tiny spikes with five to ten sporangia. This plant is most
likely r-selected, completing its whole lifespan in a short time, and such
a strategy contributes to reproduction in a suitable window time. By
contrast, most other species of Zosterophyllum and the zosterophyllopsids
on a broader scale are larger in body size and have greater investments in
fertile tissues reflected in the size and total number of sporangia. We
argue that the zosterophyllopsids probably benefited from the divergence
of various life history strategies and thus constituted a major part of
the Early Devonian floras.

植物演化出不同的生活史策略以应对有限的可用资源；然而，早期陆生植物中分化的有性生殖策略何时及如何演化尚不清楚。作为早期陆生植被中显著且重要的组成部分之一，工蕨纲（Zosterophyllopsida）及其模式属工蕨属（Zosterophyllum）在布拉格期（早泥盆世；约4.108亿至4.076亿年前）达到物种多样性的峰值。本文基于采自中国贵州省都匀市布拉格期莽山组的保存完好标本，描述了一个新种——宝阳工蕨新种（Z. baoyangense sp. nov.）。该新种植物的特征为体型微小、具K型分枝，以及带有5至10个孢子囊的小型穗状结构。该植物极可能属于r选择（r-selected）类型，其整个生命周期在短时间内完成，这种策略有助于在适宜的窗口期进行繁殖。相比之下，工蕨属的大多数其他物种以及更广泛范围内的工蕨纲植物体型更大，且在生殖组织上投入更多——这体现在孢子囊的大小和总数上。我们认为，工蕨纲植物可能得益于多种生活史策略的分化，因此构成了早泥盆世植物群的重要组成部分。