The houses were originally built on mangrove poles or ironwood posts set into the river mud. Like most traditional building materials in Southeast Asia, kayu bakau (Rhizophora mucronata), the most common mangrove tree in Brunei, has numerous uses. A boiled extract of the bark, known as cutch or gambier, yields a valuable dye used in the tanning of leather, but bakau is now used primarily as support posts for rein-forced-concrete formwork. Daun apung, the frond of the nipa palm, was the other standard building material. The fronds provided covering for roofs and walls, and the palm tree itself was a valuable source of gula anau, a deliciously heady brown sugar that is still available in the street and floating markets.