Cephalium

thumb|Cephalium atop Melocactus matanzanus A cephalium is a growth that occurs in cacti at sexual maturity, that exhibits periderm development, reduced photosynthesis and denser spine production. The boundary between the juvenile plant and the cephalium is almost always a discrete one. Cephalia have historically been defined to occur only at the tips of the plant, although does not reflect the variety of sexual transition among species.

== History and etymology == The true origin of this word is unknown, though the word was first used by William Jackson Hooker without any elaboration to describe Melocactus intortus. However, he also used the word to describe the hair flower buds of cacti such as Echinopsis, which currently are not considered cephalium-bearing. According to Karl Moritz Schumann, the genera Melocactus and Cephalocereus—which by today's standards does not bear a true cephalium— are the only genera that have cephalia. Facheiroa and Micranthocereus have also been classified as cephalium-bearing cacti. Alwin Berger, Nathaniel Lord Britton and Joseph Nelson Rose consider Discocactus and Melocactus to be the only true cephalium-bearing cacti. Few even consider the areoles of Neoraimondia and Neoabbottia as cephalia.