I grew a great many Melocactus a number of years ago and had a collection consisting of mature plants of just about every species available at that time that I grew from seed and housed in one of Dan Bach's Nursery greenhouses. Here is a pic of part of that collection (with a couple of Discocactus thrown in):
Caveat: I dug that pic out of an archived folder on my PC. The quality (resolution) isn't very good because it was taken before the advent of widely available digital cameras.
I experienced a big setback with my collection in 2011. I had a botched abdominal surgery (snipped lower intestine) that left me attached to a wound-vac machine for two months followed by a long recovery. That put me out of action in moving around my cacti and taking care of them in general. Unfortunately that time period coincided with some of the coldest weather ever recorded in Tucson: 18°F (-8°C) successive nights followed by below freezing days. The thermometer at my home registered 14°F (-10°C) one night. I was able to accommodate most of my small Brazilian cereoid cacti, Arrojadoa, Micranthocereus and Arthrocereus, indoors at my home, but most of my Discocactus (except for Discocactus placentiformis), Melocactus and Uebelmannia in particular did not survive the cold in the unheated greenhouse I housed them in (I believe the temp got down to the low twenties F at night there). That part of my collection was decimated. I couldn't expect, nor did I want, Dan to commit resources to save my plants - he had his own vast commercial growing enterprise to take care of.
As a consequence of that episode I have relatively few Discocactus, Melocactus and Uebelmannia left in my collection. Here is what the remnants of that collection looks like today (with a few odds and ends):
As you can see I lost many plants and many others were badly scarred, but one that did survive was this mature Melocactus acunae (syn. M. harlowii) which is a very rare Cuban species - and one of my favorites. Not only did it survive, but it has flourished and produces bountiful flowers and fruit:
Just one flower this afternoon:
