Peppers, to me, exude tropical heritage. Those tiny fleshy flowers and deep shiny green leaves shout, "I'm from a warm, wet forest!" I am no expert on peppers, not like my blog-friend Michelle, but I've learned a lot in the past few years I've been saving seed. Since it is important to not only know the variety one is growing when saving seed, but also the species in order to prevent cross-pollination, I picked up a few tricks to identify the four most commonly grown species. I hope someone else may find this information helpful.
Capsicum annuum: C. annuum holds most of the peppers with which we're most familiar. Our sweet bell peppers fall in this species, as do Anaheims and jalapenos, serranos and pasillas. Many people never grow anything other than annuums in their gardens. Annuums have white flowers with yellow or blue stamens and foliage that is usually smooth, though can occasionally be softly downy. The foliage is typically dark green, but there are variegated varieties; in fact, if a plant is variegated, it is likely a C. annuum. There is a huge variety in flavor within this species, from completely sweet to searingly hot. This year, I grew Fish, Chile Rayado, Big Jim, Sweet Cherry, Pimento, Lipstick, and a couple other annuums that weren't as successful as these reliable varieties.
Capsicum baccatum: I am biased. Capsicum baccatum is my favorite pepper species. The plants reliably overwinter for me, get huge (tree-like, folks!), and have bright green leaves and pretty, yellow- or greenish-brown-dotted flowers. I gave a coworker some seeds for Capeau de Frade, she planted one of her seedlings in our school garden, and the plant is three years old now and four feet tall. The three varieties I have growing are all on the milder side, though if you pop the whole thing in your mouth as I have done occasionally while working in the garden, you might find yourself sweating on a cold day. I enjoy the tropical fruit flavor of the baccatums as well as their excellent crunch factor. I have Capeau de Frade, Dedo de Moca, and some kind of orange-form Aji Panca (mislabeled seeds? a happy accident because I love this plant) that are each three years old and still growing mightily in a large pot. I cut them back in late winter so they'll send up nice growth with a dose of sunshine, spring warmth, and liquid seaweed. I am very interested in learning more about this species and exploring more varieties within it.
Capsicum chinense: C. chinense is home to the world's hottest peppers. Ghost pepper, Bhut Jolokia, all the habaneros, and others are C. chinenses. But they're not all hot. Cheiro de Recife and the like have the same citrusy, perfumy flavor without the heat (or at least not as much of it), and are gorgeous fruits, shiny and bright colored. The flowers are small and white, pale yellow, or pale green with blue stamens. The leaves tend to be bright green and slightly savoyed. These peppers are what give Caribbean food its kick. I have a harder time getting this species growing healthily than other other species, but I always grow a couple because the fragrance is impossible to beat. This year, I am growing Roberto's Cuban Seasoning and Cheiro de Recife.
Capsicum pubescens: This is the first year I have grown C. pubescens and I have not yet tasted it. However, despite my lack of familiarity with it, I'd have an easy time identifying it anywhere. Not only does its hairyness live up to its Latin name, but unlike any other species, it has large-ish purple flowers. Purple flowers! And the fruit is thick-fleshed like a mini-bell pepper, but very hot. Also unique to this species are the dark brown to black seeds. I don't know if there is much difference between varieties within this species, but the variety I'm growing is called Red Rocoto.