Evolutionary characteristics are traits or features that have evolved over time in a particular species or group of organisms. These characteristics often provide advantages that help the organism survive and reproduce in its environment.

In the case of Selaginella, an evolutionary characteristic is heterospory. Heterospory is the production of two types of spores, microspores and megaspores, in the same plant. This is in contrast to homospory, where only one type of spore is produced.

Explanation of Heterospory in Selaginella:
Heterospory is considered an important evolutionary adaptation because it allows for the production of different types of spores, which in turn give rise to different types of gametophytes. The gametophytes produce male and female gametes, allowing for sexual reproduction.

1. Advantages of Heterospory:
Heterospory provides several advantages to Selaginella and other plants that possess this characteristic:

- Efficient Reproduction: Heterospory ensures that the male and female gametes are produced in separate structures, reducing the chances of self-fertilization and promoting outcrossing. This increases genetic diversity and the potential for adaptation to changing environments.

- Enhanced Dispersal: The two types of spores, microspores, and megaspores, are typically dispersed by different mechanisms. Microspores are often wind-dispersed, while megaspores may rely on other means such as water or animal dispersal. This increases the chances of spore dispersal and colonization of new habitats.

- Resource Allocation: Heterospory allows for the specialization of the two types of gametophytes. The male gametophyte, derived from microspores, produces male gametes (sperm), while the female gametophyte, derived from megaspores, produces female gametes (eggs). This specialization enables efficient allocation of resources and increases the chances of successful fertilization.

2. Presence of Ligule:
The presence of a ligule is not directly related to heterospory but is another characteristic of Selaginella. A ligule is a small, tongue-like projection found at the junction between the stem and the leaf sheath in some plants. It is believed to have multiple functions, including protecting the meristem and regulating water movement.

3. Other Characteristics:
While not mentioned in the question, Selaginella also possesses other evolutionary characteristics such as heterophyllous habits. Heterophyllous habits refer to the presence of different types of leaves on the same plant. This adaptation allows the plant to optimize its photosynthetic efficiency and adapt to varying environmental conditions.

Overall, heterospory is a significant evolutionary characteristic found in Selaginella. It provides advantages such as efficient reproduction, enhanced dispersal, and resource allocation, contributing to the success and adaptation of the species in its environment.