We know because the germplasm hasn't had time to develop markers that are distant enough to support that hypothesis. Chances are that hemp was brought with. But there is no hemp chordage culture that developed. And the current drug type germplasm is Asian with a westward distribution. (the following is a joke, don't quote me: it's why they called it journey to the west, not to the east
Taíno: Indigenous Caribbeans
The Taíno were an Arawak people who were the indigenous people of the Caribbean and Florida. At the time of European contact in the late 15th century,www.blackhistorymonth.org.uk
"The Taíno were an Arawak people who were the indigenous people of the Caribbean and Florida. At the time of European contact in the late 15th century, they were the principal inhabitants of most of Cuba, Jamaica, Hispaniola (the Dominican Republic and Haiti), and Puerto Rico.
In the Greater Antilles, the northern Lesser Antilles, and the Bahamas, they were known as the Lucayans and spoke the Taíno language, a derivative of the the Arawakan languages.
The ancestors of the Taíno entered the Caribbean from South America. At the time of contact, the Taíno were divided into three broad groups, known as the Western Taíno (Jamaica, most of Cuba, and the Bahamas), the Classic Taíno (Hispaniola and Puerto Rico) and the Eastern Taíno (northern Lesser Antilles). A fourth, lesser known group went on to travel to Florida and divided into tribes. At present, we know there are four named tribes; the Tequesta, Calusa, Jaega and Ais. Other tribes are known to have settled in Florida, but their names are not known.
At the time of Columbus’ arrival in 1492, there were five Taíno chiefdoms and territories on Hispaniola, each led by a principal Cacique (chieftain), to whom tribute was paid. Ayiti (“land of high mountains”) was the indigenous Taíno name for the mountainous side of the island of Hispaniola, which has retained its name as Haïti in French."
Let's allow us to assume that these Caribes natives (vastly coming from northen of South America, Amazon not the Andes) had their own narrow leaf variety, as its impossible that broad leaf varieties ever set foot in the Americas (at this time).
Edit:
My point is; We know around what time the "Indian hemp" came to the Americas and Caribe.
What we dont know is the Natives peoples side of the story, as data shows most of the "history" on the Americas is colonial based. Its naive to think that a place like the Amazon would not have its own genotype of Cannabis coming from Asia dating back to the peoples crossing the Bering Strait, later settelling everywhere North, Central and South.
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