Those readers who know me in real life probably know by now what a herbarium is, since I work with them every day. For the rest, think of a herbarium as a sort of reference library for plant specimens. Botanists go out and dig up or clip off samples of plants, then press them flat between newsprint and blotting paper, folding or clipping them to size if they're too large to fit in the press. The pressed, dried specimens are glued to 11x17" sheets of archival paper, given detailed labels, and filed in the herbarium's cabinets for later reference. In those dark, dry, cool cabinets, a properly-prepared specimen can last for literally hundreds of years.
Think back for a moment over that process, and you'll realize that by the time it's archived, the plant on a specimen sheet is well and truly dead. Dug up, washed off, sliced up, pressed flat, dried out, glued down, and then locked away in the dark for long stretches -- well, how many plants do you know of that can bounce back from that?
To my great surprise, I actually met one not long ago.
In the wild, Mammillaria tetrancista -- the common fishhook cactus -- looks like a fat green cylinder densely studded with inch-long, hooked, needle-thin spines. On the herbarium sheet, it's still green on the outside, but the cut surfaces of its stems are vibrant Crayola shades of red and orange. Live or dried, it's a rather striking sight.
When I pulled out a folder of M. tetrancista last month, though, I got a surprise that had nothing to do with color or spines. The specimen inside was over a year old, collected and dried in the summer of 2010. It should have been desiccated and preserved. Instead, it was sprouting.
Source: CIC Herbarium