twins.object

The objects of class <code>"twins"</code>
  represent an agglomerative or divisive (polythetic) hierarchical 
  clustering of a dataset.

cluster

Functions for cluster analysis, originally from
  Peter Rousseeuw, Anja Struyf and Mia Hubert.

This class of objects is returned from <code>agnes</code> or <code>diana</code>.

The <code>"twins"</code> class has a method for the following generic function:
  <code>pltree</code>.

The following classes inherit from class <code>"twins"</code> :
  <code>"agnes"</code> and <code>"diana"</code>.