Actually it's a blend from the Anguttara Nikaya (AN 4:133), in the Ugghaṭitaññu Sutta about four types of persons classified according to their ability of acquiring insight and Bodhirājakumāra Sutta (MN 85), simile of 3 kinds of lotus.
If you read Thai you can find more info on:http://th.wikipedia.org/wiki/%E0%B8%9A% ... 8%E0%B8%B2http://84000.org/tipitaka/attha/attha.php?b=21&i=131
In English on http://www.accesstoinsight.org/glossary.html#u
Of swift understanding. After the Buddha attained Awakening and was considering whether or not to teach the Dhamma, he perceived that there were four categories of beings: those of swift understanding, who would gain Awakening after a short explanation of the Dhamma; those who would gain Awakening only after a lengthy explanation (vipacitaññu); those who would gain Awakening only after being led through the practice (neyya); and those who, instead of gaining Awakening, would at best gain only a verbal understanding of the Dhamma (padaparama).
Or in the book Requisites of Enlightenment by Venerable Ledi Sayadaw, downloadable at http://www.bps.lk/olib/wh/wh171.pdf
Page 5 - Four Types of Capacity for Path Attainment
Regarding the lotus simile:http://tipitaka.wikia.com/wiki/Bodhirajakumara_Sutta
Like in a set of blue lotuses, red lotuses and white lotuses, a certain one would be born in the water grow and develop in the water and would bloom below the level of the water. Some others would be born in the water grow and develop and bloom in the level of the water and certain others would be born in the water, grow and develop and stand right above the water and bloom. In the same manner I saw beings with little defilements and much defilements, with sharp mental faculties, and weak mental faculties, with good dispositions and weak dispositions and certain ones fearing the other world.
This describes only 3 categories of lotus, the fourth is an elaboration of this sutta (according to the Thai wikipedia page).
On for instance http://dhammalikeyou.blogspot.com/
I find the following:
The fourth personality (padaparama), the fools, the idiots, who are unteachable (อเวไนยสัตว์ / aveneya satta). In other words they are the people the Buddha had nothing to do with.
They are like lotuses that are very deep down in the water, so deep that there is no way they will rise above the surface because they fall food to fishes and turtles.
This fourth category I can still, however, find no official English language resources about. So I don't know in which sutta this fourth category of lotus was described.
On the other hand, there's a lot of information in Thai language.