The hau is found along the rivers and roads here.  Especially from the Wailua river to the North shore.. I've always been intrigued with its remarkable flower that changes color three times in a day. In the morning it is bright yellow, in late afternoon it changes to apricot and just before dusk it takes on an orange hue before dying and falling off.  I bought one for my yard in Corpus and it grew extremely tall.  It was labeled as an Hawaiian Green Hibiscus.  I have since found that hau means a large shrub or tree.  It was not named specifically for it's type.  It's scientific name is Hibiscus tiliaceus.  I have also found it called Sea Hibiscus (and never documented as Hawaiian Green Hibiscus) as it is well adapted to salt air and water.

Uses: The Hawaiians used the inner bark of the hau plant to make a cord. The cord was used to make handles for gourds, to tie the covers of lauhala baskets, to sew kapa bed sheets together, and to tie sandals on their feet. The cord was dipped into dyes to make kapa designs. It was also used to make weapons like a slingshot and to tie points on spears. 

This plant was considered very valuable and permission was required by the village chief to cut it.

One legend says that hau is a sister of the goddess Hina, changed into a tree. The people of Tahiti say hau is the grandchild of heaven and earth. Some people equate the brief span of the hau flower as representative of the transitory nature of human life.

Sometimes, Hawaiians would use a block of soft hau wood and a pointed stick of a hard wood, rubbed together to make fire.