The upward growing breathing roots of mangrove plants are called:

The correct answer is A, pneumatophores. Mangrove mud is waterlogged and short of oxygen, so these roots grow vertically out of the soil and take in air through small pores called lenticels; they are the classic adaptation asked about in examinations, along with stilt roots and vivipary. Option B is wrong because haustoria are the absorbing organs of parasitic plants such as Cuscuta, which draw food from a host, a matter of parasitism and not of respiration. Option C is wrong because velamen is the spongy covering on the hanging roots of epiphytic orchids, which absorbs moisture from humid air and belongs to a very different habitat. Option D is wrong because a tap root is the ordinary single main root of a dicotyledonous plant and has no special role in breathing. Remember the trio for mangroves: pneumatophores, stilt roots and viviparous seeds.