The graphic shows the island of Krakatoa, which disintegrated in 1889, due to the largest volcanic eruption in recorded history. In the century since the eruption, the island has re-formed from lava flows. The table above shows the number of species of various plant types that were found on the island over a 30 year period, since the island re-surfaced above the ocean in the 1950's. Which of these plants is likely to be a pioneer species?