Correct option is A
The order Psilotales is best identified by its leafless and rootless body with a dichotomously branching stem. Psilotales is a group of primitive vascular plants that include the genus Psilotum, commonly known as whisk ferns. These plants have a simple structure, with a stem that branches dichotomously (splits into two) and no true leaves or roots. The absence of typical leaves and roots, coupled with the dichotomous branching pattern of the stem, is a key characteristic of this order. They are considered a basal group of vascular plants and are one of the most primitive living vascular plant groups.
Information Booster:
- Psilotales represent an ancient lineage of vascular plants that still exhibit some of the most primitive characteristics found in early vascular plants. They lack roots, leaves, and vascular tissue differentiation found in more advanced plants. Their dichotomously branching stems and their simple structure (with only photosynthetic stems) are considered primitive traits that were possibly inherited from the earliest vascular plants that evolved in the Silurian period.
- The lack of true leaves and roots in Psilotales makes them an interesting subject of study for understanding the early evolution of vascular plants.
Additional Information:
- Very large fronds, some reaching 4.5 m or more in length: This characteristic is typically associated with ferns from other orders such as Polypodiales, not Psilotales. Psilotales do not have large fronds; rather, they have small, scale-like structures.
- Scale leaves that are borne in whorls at the node: While Psilotales have scale-like structures, they do not bear these leaves in whorls, but rather in a more simplified manner along their stems. This characteristic is more specific to other groups of plants, such as Lycopodiaceae (club mosses).
- A plant body that consists of microphylls and roots only: Psilotales do not possess microphylls (small leaves) or roots. This is a trait of other plant groups such as Lycophytes, not Psilotales.
