Mike Stocklin in South Dakota, one of the bowyers that did the stuff for Dances With Wolves, has made some buffalo killer Sioux style horse bows backed with sinew and hide glue. He has had no problem hitting 65-70 lbs with these bows at as little as only 36 inches!
His technique is to split the rattan down the middle on a bandsaw, add some nocks, then start with the cut side to the back, and tiller on a belt sander while the bow is strung. Once tillered just below your final weight, he heats in the recurves and decurves he likes and lays up the sinew. Of course it is a little more than that, but you get the drift.
There was an article a long time back in PA on rattan bows. Quite a few people used it for making quickie kids bows, but there is plenty of potential for adult weight hunting gear with this grass.