In an alternate Earth, early or midway in the Eocene Epoch, there debuted a family of angiosperm trees whose roots need to be completely submerged. As a result, the limit is that they can't germinate in waters that dry up during low tides, nor can they at depths deeper than 250 feet. Such trees with roots that need to be submerged 24/7 could have easier, more efficient water transportation, allowing them to grow taller even than the redwoods. The tallest tree on this alternate Earth, the ash-like yggdrasil, averages 150 meters tall and 12 wide, with crowns averaging 180 feet wide and branches 13 feet wide.
To compensate for this large size, the yggdrasil's roots extend as far out as 400 feet. As mangroves, they are expected to be supported by "aerial roots"--that is, roots that grow above the soil. There are many different kinds of aerial roots--stilt, knee, pencil, cone, buttress and spreading. Of those shapes, which ones would be best at supporting a megamangrove tree, particularly one as large as an yggdrasil?