Koko Head Lookout-Oahu
Photo Kim and Forest Starr
Native of Brazil, Ecuador, Peru and Venezuela, Alternanthera pungens is a major weed of warm temperate and tropical areas around the world; widespread in wasteland, parks, orchards and recreation areas.*
In Hawaii, according to an agent at HEAR (Hawaii Ecosystems At Risk) the weed is widespread, and considered 'naturalized'. On Oahu, judging from varying concentrations of infestations, island wide, it looks as though the species propagated from the Diamond Head area--where concentrations are relatively high. [That is just my guess.] There are reports of infestations in the Diamond Head area dating from the 1970s.
Khaki weed frequently sprouts near walkways and in public parks, where its seed-burrs are tracked by human traffic. Some public-school campuses are heavily infested, which should be of serious concern.
It is also widespread on the island of Maui. Significant infestations on the island of Kauai are confirmed, as well. [I don't know about the other islands.]
Some sources note, Khaki Weed "prefers light soils, warm temperatures and plenty of moisture"* But as we see by the photo (above), taken at Koko Head lookout, on Oahu, this weed is also happy basking on hot-dry gravel, under salt spray. It also spreads surreptitiously beneath the level of mowed lawn.
If weeds are considered "the pioneers" of the plant kingdom, then Khaki is the pioneer of pioneers. It flourishes in the densest dirt where other common weeds refuse to root. In temperate climates, khaki weed is seasonal. In Hawaii it grows all year round.
In summery, as far as Hawaii goes, Khaki weed grows wherever it wants...whenever it wants
* Reference
Government of South Australia; Animal and Plant Control Commission; Weed Identification Notes [pdf]and
http://www.mitchamcouncil.sa.gov.au/webdata/resources/files/khaki_weed_control1.pdf
