[whyenot]

There is more than one plant with the common name "mother-in-law's tongue." I think OP might have been referring to Dieffenbachia sp. which is a tropical rainforest understory plant and does very well in the low light conditions of an office. [It's leaves contain very large amounts of oxalic acid which is probably why it got the name -- eat the leaves and your tongue swells up and you can't talk anymore...]

[andyjohnson0]

In the UK, "Mother-in-law's Tongue" usually refers to Sansevieria trifasciata [1]. The plant being sharp and pointed, the name is presumably an un-PC reference to the archetypal "domineering mother-in-law".

[1] http://en.wikipedia.org/wiki/Sansevieria_trifasciata