Alright you guys. I'm very busy these days so it might take me a while to get to you.
I really don't have many small plants so I'm not really a very good source for the answer to your question but I will tell you what I do know.
There are small plants that will stay small no mater what and there are plants that will adapt to their container very well and stay small in a small pot with limited fertilizer and still flower well. Many medium size plants will stop blooming if they don't get enough fertilizer even though they might stay small in a small pot and of course a huge plant like Mayla might be ruled out for bonzaing, if that’s a word, just because it's big to begin with and would jump the pot quickly.
Of the commercially grown plants that I have that are known to be small I would rate Perry's Baby red near the top.
It is not only genetically small but it is highly adaptable to a bonsai situation and is just great. On the bottom of the list I would have to put Chrysantha. It is a rapid producer of tons of dormant crowns and even in a mud pond it almost never flowers. I really do like Ladekery Fulgens. It is very slow to grow but seems to do well in a bed with low fertility.
There are so many small plants that I don’t have and the ones that I do have, because they are small just sit back in the spike rush and I really don’t know them well enough to give a good opinion on them. I like Vesuve and I think it is supposed to be small. Also Colorado. I'm not sure what the definition of small is exactly but I think Colorado in a small pot would qualify.
At the risk of sounding like I'm always pushing my own plants I have a few that I really like that stay under 2 ft dia. in very fertile big pot conditions but I don’t know how well they would do in bonsai conditions because I have never grown them like that but I do know that they are genetically very small.
The first pic is Hunnycup. Nearly the whole plant is visible in this pic. Only about three old dieing leaves are not visible in The lower right. Very controlled growth and slow to make offsets. No more than 2 ft across.
The next two are 57,06, no name yet. A pretty amazing plant actually and I don't think I have shown this one before.
The plant is the same size as Hunnycup but the flower is HUGE for such a small plant. It's a not bad run of the mill light pink color and it fades very little. I have not measured the flower but I guess that it is 6-7 inches in dia at it’s biggest and the flowers are never under 5 inches. It has lots of petals and an extremely high flower to leaf ratio.
I have very few plants of this so far because it's such a slow divider and I haven't had time to work on it but I think a bed of it would be spectacular.
Another run of the mill pink colored flower similar to Colorado in that it starts the year a nice salmon pink that fades to a very light, not to attractive pink as the year progresses. I like it though because it is a 6 inch flower with the thinest petals of any lily I know of on a very small plant with very few leaves that show more water and are more leggy than Hunnycup or 57,06 but less leaf surface area per flower volume I would say. I have no idea how well it bonsais but it does very well in crowded conditions and just keeps on flowering. The leaves are thin and flexible like Colorado leaves and very lightly marbled when young like Colorado.
All three of these plants are being tested in Texas this year so I will have more info later on how they like the heat.
So far according to Ken Landon all of my plants stand the acid test in blazing hot 105 degree west Texas heat, Flowers " as big as dinner plates " in 2 gallon pots, and I expect that these will also.