There are at least 4 species of Pontederiaceae in the Tempisque River basin. Here is one: Heteranthera limosa, a small, emergent plant inhabiting well lit, recently flooded, shallow areas of wetlands.  The entire plant is relatively delicate, perhaps as a result of fast growth.  Unfortunately, I didn’t catch any with flowers open – it may occur during a certain time of the day, because I did see this open earlier in the morning.