Drynaria rigidula -- An epiphytic fern of S. E. Asia.  This fern is commonly known as the Oak leaf fern. It has two types of fronds -- one fertile (once-pinnate), the other sterile (broad shield). There is a cultivar of this fern, Drynaria rigidula 'Whitei' which has pinnae which are highly serrated and not smooth as the species.  However, D. rigidula 'Whitei' is not a fertile plant and it is only propagated through divisions.

In the world of ferns, there are terrestrial (ground grown), lithophytic (rock grown) and epiphytic (tree grown) ferns.  The ferns are found growing on trees, are generally epiphytes.  While these ferns live on trees, they do not live off of trees.  There is a symbiotic relationship that keeps the two entities separate.  Ferns are not parasitic and generally do not harm the host tree.  In Southeast Asia, occasionally an epiphytic fern e.g. Aglaomorpha heraclea or Asplenium nidus (Bird's nest fern) may grow too large for a branch, the sheer weight of the fern will cause the branch to break, bringing the fern down with it.