Botanizing in Hawaii: Solanum linnaeanum

Hawaii has a long history of biological invasions. Plants and animals from all over the world have arrived and thrived there under the tropical sun. This can make it somewhat difficult to identify a random plant, because it could literally come from almost anywhere on the planet.

On one of my hikes, I found several plants I immediately recognized a member of the family Solanacea. This is the same family that includes tomatoes, peppers, and eggplants. I was pretty sure it was even a member of the genus Solanum, one of the several species sometimes referred to as "spiny eggplants".

 I collected a few fruit, intending to secure some seeds for planting back home in Minnesota. A couple days later, while sorting through my collection at a motel, I finally identified the plant as Solanum linnaeanum. Among its various common names are: "Poison Apple", "Devil's Apple", and "Apple of Sodom". They're native to parts of southern Africa, but have naturalized in Hawaii and various other places around the world.


The plant and its fruit are chock-full of toxins. Enough so that very few animals are willing to eat it. At about this point I decided not to take seeds home for garden trials. I do have a few seeds in my collection that come from highly toxic, or otherwise dangerous, plants. I wasn't entirely certain how much difficulty I would have with trying to leave Hawaii with collected seeds. If some official asked me what they were and why I had them, they might not appreciate my responses. So, to limit that risk, I dumped the S. linnaeanum seeds in the garbage.

(Several days later when I left the state, I learned I would have had no trouble at all. Dried seeds in vials didn't concern the USDA officials at the airport at all. Bringing seeds into Hawaii gets their attention, not taking seeds away from Hawaii. Next time I'll be a bit more bold.)

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Interestingly, it appears this species can cross with domesticated eggplant (S. melongena). Doganlar et al. studied an F2 population derived from a cross of the two species in order to map the genomic positions of genes for traits important in domestication. Unfortunately, their paper doesn't have any photos of what the F2 plants looked like. Even with the risk of dragging the toxic traits from S. linnaeanum into the progeny, this would be a fun cross to recreate and explore. The wild species probably has numerous disease/insect resistance traits that would be useful in a garden eggplant, so there is probably value to the experiment beyond simple personal amusement. There's a few online vendors offering seed for this species, so I won't have to make another trip to Hawai'i to start on this project.


References:

• http://www.starrenvironmental.com/images/search/?q=Solanum+linnaeanum
• https://www.ctahr.hawaii.edu/invweed/WeedsHI/W_Solanum_linnaeanum.pdf
• https://en.wikipedia.org/wiki/Solanum_linnaeanum 
• http://www.genetics.org/content/161/4/1713