A characteristic feature of bryophytes is

The correct option is: "a small sporophyte phase, which is dependent on the gametophyte"

To understand why this is a characteristic feature of bryophytes, let us break down their life cycle and structure step-by-step:

1. Alternation of Generations:
Like all land plants, bryophytes (which include mosses, liverworts, and hornworts) exhibit an alternation of generations between a haploid gametophyte phase and a diploid sporophyte phase.

2. Dominant Gametophyte Phase:
In bryophytes, the green, photosynthetic, and independent plant body that we commonly see is the gametophyte. This phase is haploid (contains one set of chromosomes, denoted as $n$) and is responsible for producing gametes (sperm and egg cells). It is the dominant, long-lived, and structurally independent phase of the life cycle.

3. Dependent Sporophyte Phase:
The sporophyte phase is diploid (contains two sets of chromosomes, denoted as $2n$) and develops from the zygote inside the female reproductive organ (archegonium) of the gametophyte. Unlike vascular plants (like ferns, conifers, and flowering plants) where the sporophyte is dominant and independent, the bryophyte sporophyte is small, physically attached to, and nutritionally dependent on the parental gametophyte for water, mineral nutrients, and often photosynthates throughout its entire existence.

4. Analyzing the Incorrect Options:
• "a dominant and parasitic sporophyte": The sporophyte is dependent (parasitic in terms of nutrition) on the gametophyte, but it is not the dominant phase.
• "a dominant and spore-producing gametophyte": While the gametophyte is dominant, it produces gametes (sex cells) rather than spores. Spores are produced by the sporophyte.
• "sporophytes stay for a longer duration": The sporophyte phase is transient and short-lived compared to the persistent gametophyte phase.

Therefore, the presence of a physically small sporophyte phase that remains permanently attached to and dependent on the dominant gametophyte is the defining characteristic feature of bryophytes.