I was reading about agaves in my new Monocotyledons book, which I can recommend if you can find it at a sane price. The author of the agave chapter (J. Thiede) provided these factoids in the intro to the genus...
There are approx. 265 agave species (at the time of writing, after the genus expanded). Greatest richness is in Puebla-Oaxaca in southern Mexico. (Not coincidentally where they also celebrate mescal and pulque.)
Subgenus Agave (with the branched inflorescence) is concentrated in S. Mexico, Subgenus Littaea in E. Mexico, Subgenus Manfreda in W. Mexico and N. Oaxaca. As a random quirk of semantics, the word "panicle" is often used to describe the branched inflorescences (Agave), but it turns out the unbranched ones are also panicles, in the botanical definition of the word, if you look at the way the nodes are put together along the stem. So maybe avoid that word or use it for all agaves, to the extent it matters.
Constitutive (always on) CAM metabolism is almost always present in the first two subgenera (the genus before it was expanded). Data lacking elsewhere. That means they breathe at night and hold their breath during the day. Our nighttime humidity is usually in the 90s (%) because of the coastal breeze, I would think the agaves enjoy that.
Like Yucca, Agaves often have rain roots, which are an interesting temporary structure near the stem which allows them to get the most of rain events that are widely spaced in time. I don't know whether they occur in containers but they're said to be very important in the landscape.
The vegetative phase lasts from 6 to 55 years (in nature, presumably). Park Nobel (who wrote a whole book on environmental biology of these plants) showed with a population of Agave lechuguilla that about 4% of the population flowered in a peak year, less than 1% a year later. These differences are related to the number of wet days in the 2 years prior to flowering. So the plant apparently decides based on water availability. About 2/3 of the energy stored by the plant goes into flowering; the water required for flowering is stored within the leaves (no additional water required).
Some of our native agaves flower early, which means late fall (most of them do it during winter). In dry years that means they will put up a full size inflorescence and all the accoutrements, and be fully flowering when they haven't had a drop of rain in 8 or 9 months. It is very impressive, and provides a sharp contrast against the otherwise brown landscape (at that point).
