How do temperature and environmental conditions affect male and hermaphroditic horsetail gametophytes?

In the life cycle of horsetails (Equisetum), environmental conditions—specifically temperature—play a significant role in determining the sexual expression of the gametophytes.

While these plants are homosporous, they produce two distinct types of gametophytes: smaller, male-only gametophytes and larger, hermaphroditic ones. The ratio of these types is not fixed and can be altered by environmental factors:

• Temperature: Research indicates that temperature is a key driver of this sexual differentiation. For example, at higher temperatures, such as 32 °C (about 90 °F), spores develop exclusively into male gametophytes. In contrast, at cooler temperatures, such as 15 °C (59 °F), the population is more balanced, with approximately 50 percent developing as male and 50 percent as hermaphroditic.1

These shifts in sexual expression demonstrate how environmental plasticity allows horsetails to adapt their reproductive strategy based on external conditions.1