Final answer:
Most ferns have an underground stem known as a rhizome, which supports leaves and serves multiple functions. This is particularly true for species like wood ferns with clustered leaves emerging from hidden rhizomes, making the statement true.
Step-by-step explanation:
The statement that most ferns have underground stems is true. Ferns typically possess an underground stem known as a rhizome, with fronds emerging from this rhizome. The rhizome is a critical component, serving not only as support for the leaves but also as a means for asexual reproduction and storage of nutrients.
In many species, like wood ferns, the rhizome produces tight clusters of leaves that create a circular, urn-like arrangement. Others have rhizomes that grow more horizontally, spreading to form a uniform patch of ferns. There are also examples such as tree ferns with vertical stems, or aquatic and clover-like ferns with distinctive growth forms.
The dominant life stage of ferns is the sporophyte, which features the visible fronds that are key for photosynthesis and reproduction. These fronds originate from the rhizome, which may be woody and exhibit secondary growth. The rhizome can live for many years, with new fronds emerging each season.
Your final answer is true: most ferns indeed have underground stems called rhizomes that serve various functions, from supporting the fronds to storing nutrients and facilitating asexual reproduction.