P. mello-barretoanum may look like your garden-variety P. bipinnatifidum (selloum) but on closer (careful) inspection of the trunk, one of the most distinguishing characteristics becomes evident. Unlike P. bipinnatifidum varieties, this plant has genuine hard thorns on the trunk, as shown in the picture below.
The plant grows quite large if cultured properly, and the leaves, while bipinnately cut, are not ruffly, undulate, or sinuate on the margins as are most varieties of P. bipinnatifidum.
This plant is one of those that does not grow at all when the weather is relatively cool. Temperatures in the 70 degree F and below range will bring this plant to a standstill, and growth will not resume until the 80 degree days return.
We crossed this plant successfully with P. goeldii but our first attempt was lost to the flooding from hurricane Katrina. We repeated the cross in 2006 and now have 5 very healthy plants from that work.