As described in Section 28.2 one proposed bryophyte...

As described in Section 28.2 one proposed bryophyte phylogeny considers hornworts and vascular plants (such as lycophytes and ferns) to be sister clades. Among other factors, a shared morphological feature supports this hypothesis: hornwort and vascular plant sporophytes both show indeterminate growth-once a sporophyte develops, it grows for the remainder of the plant's life. Indeterminate growth has not been observed in other bryophyte lineages. Can you think of a different evolutionary explanation for the growth pattern shared by hornworts and vascular plants?

Key Concepts

Phylogenetic Analysis and Homoplasy

Phylogenetic analysis involves reconstructing the evolutionary relationships among different species based on genetic, morphological, or developmental data. When a trait like indeterminate growth is found in unrelated groups, it is important to distinguish between homologous traits, inherited from a common ancestor, and homoplasies, which arise independently. Recognizing homoplasy—such as through convergent evolution—helps clarify that similarities in traits may not necessarily reflect a close evolutionary relationship but could instead be adaptations to similar environmental challenges.

Indeterminate Growth

Indeterminate growth refers to the pattern where an organism’s growth continues throughout its life instead of stopping after a specific developmental phase. In plants, especially vascular plants and some bryophytes like hornworts, this means that the sporophyte can continue to expand and differentiate over time. This concept is crucial in understanding plant morphology and life cycles as it affects how plants colonize space, compete for resources, and evolve their overall structure.

Convergent Evolution

Convergent evolution is the process whereby unrelated or distantly related organisms independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. In the context of the growth pattern shared by hornworts and vascular plants, the similar indeterminate growth could be the result of convergent evolution rather than inherited from a common ancestor. This explanation posits that similar selective pressures led to the evolution of a growth mode that confers an adaptive advantage, leading to an analogous feature in both groups.

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