/usr/lib/R/site-library/rncl/INDEX is in r-cran-rncl 0.8.2-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 | read_nexus_phylo        Read phylogenetic trees from files
rncl                    rncl: An R interface to the NEXUS Class Library
 |