Hi,
Could be the vermiculite trapped too much moisture so the petiole could not breathe. Also, the petiole should not be too long.
Two suggestions, use spring water and use perlite, not vermiculite. Recut the petiole, revive by floating the entire leaf in a small bowl of water to which you add a healthy pinch of sugar. let them stay for several hours until they are crisp. Then replant in a mix of 60% perlite, 40% potting medium. If you use vermiculite, add just a pinch.

Perlite does not retain moisture and allows the soil to aerate. Vermiculite is very fine and traps water, so it may have kept the petiole too wet. I have lost leaves when I used too much vermiculite.

Every leaf is an individual, so no two leaves might "take" exactly the same way.

In the future, when ordering leaves from Lyon's, trim them then revive them first by floating them in a bowl of spring water with sugar added. Lyon's leaves usually have a very long petiole that will need to be trimmed to 1 1/2"

By the way, I am a big fan of Lyon's. However, if you want to try other vendors whose leaves arrive in great shape, consider Donna Brining of Fancy Bloomers in NJ and
Janet Stromborg of Allegro Violets in WI. Janet Stromborg has her own hybrids and has developed a unique vacuum pack method of sending leaves. They remain crisp for a long time so they can be left in the packet for a few days. Donna Brining wraps her leaves so they stay moistened. She has hard-to-find vintage violets plus her own hybrids. Both can be found on the internet. Joanne

This post was edited by fortyseven on Thu, Nov 13, 14 at 15:22

It definitely happens at times, so you're not alone. My guess is that sometimes the leaf blade is too large for the cut end of the petiole to bring up enough water, or that the cut end is pressed against a piece of perlite, which doesn't transport water well. Either way, try recutting the leaf and putting the cut end in water. Also, put a bag over the leaf at this time to keep it humid around the leaf. If the leaf recovers you might try cutting the edges off of it so that less leaf area needs to be supported by the petiole cut. Many people do this anyway so that the leaf doesn't continue to grow. Then replant and place a bag or cover over it and hope for the best. I haven't tried 100% vermiculite as a medium, but have heard of its use.

Mark