Psilophyta, or whisk ferns, are a group of vascular plants that are considered basal within the monilophytes, a clade that includes ferns, horsetails, and whisk ferns.

Here's a simplified breakdown of their position in the phylogeny:

* Kingdom: Plantae (Plants)

* Division: Tracheophyta (Vascular Plants)

* Subdivision: Monilophyta (Ferns and Allies)

* Class: Psilotopsida (Whisk Ferns)

Basal means that they are one of the earliest diverging lineages within the monilophytes. They are considered to be primitive because they lack true roots and leaves, instead having a simple, branching stem structure.

However, it is important to note that the classification of Psilophyta is currently being revised. Some modern classifications consider them as part of a broader group, the *Equisetopsida*, which includes horsetails.

Here is a more complete phylogenetic tree showing the relationships of Psilophyta within the monilophytes:

```

Tracheophyta (Vascular Plants)

|

|

-----------------------

| |

| |

Lycopodiophyta Monilophyta (Ferns and Allies)

(Clubmosses) |

------------------

| |

Psilopsida Equisetopsida

(Whisk ferns) (Horsetails)

|

Polypodiopsida (Ferns)

```

This diagram shows Psilopsida as a separate class within Monilophyta, but as mentioned, some classifications now include it within Equisetopsida.

Regardless of the exact classification, Psilophyta remains a fascinating group of plants that provide insights into the early evolution of vascular plants.