Growing in the Oslo Riverfront Conservation Area (ORCA) parking lot amongst wild coffee (Psychotria nervosa) and last’s week’s Wednesday “weed”, beggarticks (Bidens alba), is what some folks call tropical milkweed (Asclepias curassavica). Other common names include scarlet milkweed, Mexican milkweed, bloodflower, and silkweed.
This plant definitely is weedy and has been volunteering in the ORCA area for years. Below is a photo of a julia butterfly (Dryas iulia) and a monarch butterfly (Danaus plexippus) taken in 2008 along Oslo Road back when it was uncommon to see julia butterflies this far north …
Tropical milkweed is nectar plant for lots of different species of butterflies and is a larval host plant for monarch, queen (Danaus gilippus), and possibly solder (Danaus eresimus) butterflies.
Tropical milkweed is very easy to grow, unlike our 21 species of native milkweeds which tend to be persnickety about growing conditions and germination. You frequently will see tropical milkweed for sale at garden centers.
Planting this non-native milkweed in Florida is controversial due to potential impacts on monarch butterflies. University of Florida Associate Professor Dr. Jaret Daniels believes that there is a correlation between tropical milkweed and a build-up of a protozoan parasite Ophryocystis elektroscirrha (OE), as well as a potential consequent impacts on monarch breeding during the fall migration. Some people cut their tropical milkweed back to the ground in the fall to avoid this possible problem.
Tropical milkweed is very variable in color, so please do not be fooled. The golden cultivars are still problematic …
Seek out real native species for your garden, if you can, and take care to select a species suited to your site conditions. The xeric scrub on the south side of Oslo Road at ORCA (seen below) is home to a rare Florida endemic Curtiss’ milkweed (Asclepias curtissii) that would fail to thrive in a “usual” garden setting.