I want to propose a question with some pics for comparison. All of these leaves are at close to the same point in development. You will note that 2 have significantly longer tendrils. Is the tendril length before the leaf unfurls, in any way indicative of HL or LL genetics? Would love to hear some peoples thoughts on this. Also I would be happy to see some pics from members growing specifically HL or LL plants. It would be nice to do some comparing and see if we could come up with an answer. If we found that longer tendrils prior to unfurling had a tendancy to be LL, it would be easier to presume necessary conditions, or at least a good starting point for unidentified plants that some of us may bring into our collections. I have mostly hybrids so the best pics for comparison would come from the purists.
This is my mirabilis x (rafflesiana x ampullaria) LL Hybrid, note the tendril on the unfurled leaf is between 30-40% the size of the leaf itself.
Poi Dog showing a similar ratio.
Ventrata has a significantly smaller tendril in comparison as does this other poi dog.