I live in Cosby, TN in the foothills of the Great Smoky Mountains National Park. I plant native species of wildflowers and shrubs. My question to you is: I planted cucumbers in raised beds next to the woods. When I went out to pick some cucumbers I noticed a small replica of the cucumber plant growing right in with them. This plant has a small 5 petal yellow flower which turns into a small green fruit (?) and grows on a vine that is a rapid grower. The leaves are staggered on each side of the vine (not across from each other). Will this plant cross-pollinate with my cucumbers? Is this plant poisonous? I've been eating my cucumbers and nothing has happened to me yet. I would like to hear from you regarding my questions. Thank you.
Your plant sounds like Meloncito (Melothria pendula), a member of the Family Cucurbitaceae (Cucumber Family). Other common names are Creeping cucumber or Speckled gourd. More pictures appear in the Missouri Plants database. If you would like to verify that this is your plant, you can send us a digital photo. Visit the Ask the Expert page and follow the instructions under "Plant Identification."
The Poisonous Plants of North Carolina database lists it as mildly toxic--the fruit is listed as a strong laxative. Melothria is very unlikely to cross with your cucumber; intergeneric hybrids are extremely rare. Further, even if it did cross with your cucumber, the fruit of the current generation would not be affected at all and would be completely safe to eat. Only the progeny of the cross would exhibit any characteristics of the male parent plant. So, unless you collect the seeds to replant next year or let the fruits fall for their seeds to germinate next year, you won't have a problem.
A bigger concern could be the possibility of vectoring a cucurbit virus to your garden plants. There is a virus called Melothria Mottle Virus that is hosted by Melothria plants and to which plants in the Cucumis genus (cucumbers) are susceptible. Although not too likely to happen, this virus could potentially affect your garden cucumbers, so it would probably be a good idea to keep the plants from close proximity.
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