The rubber tree (Hevea brasilienis) is the most important source of natural rubber. However, rubber trees might not be a suitable source for latex for space settlements, as it takes seven years for one tree to mature. Another issue with Hevea latex is that it contains proteins which cause allergic reactions in some people.
Though there 12,000 plant species which produce latex, only a few are interesting from a commercial perspective. After the rubber tree, the most promising sources of latex are:
Both species produce a hypoallergenic latex. Genetic engineering might be used to increase the yield of these plants. Anyway, space settlers should consider these two species as a way to achieve self-sufficiency in respect to natural rubber.