Petunia is a genus of about 35-40 species of flowering plants of South American origin. They belong to the nightshade family (Solanaceae) along with tobacco, tomatoes, potatoes and chile peppers. The Kew Plant List splits Petunia into two closely-related genera, with 17 species retained in Petunia and 28 species in Calibrachoa, including Calibrachoa parviflora. The Jepson Manual (2nd Edition, 2012) lists this native California species as Petunia parviflora. The flowers truly resemble a miniature version of our cultivated petunias. The tubular, fragrant flowers of petunias are commonly pollinated by nocturnal hawkmoths of the genus Manduca.

The folllowing quotation is from the on-line PDF of "Phylogenetic Analysis of Petunia Sensu Jussieu (Solanaceae) Using Chloroplast DNA RFLP" by Toshio Ando et al. It was published in Annals of Botany 96: 289-297 (2005).

"It is concluded that Petunia sensu Jussieu is a monophyletic clade when rooted using Nicotiana langsdorffii, and that it consists of two major monophyletic sister clades: Petunia and Calibrachoa. Two unusual Calibrachoa species, C. parviflora (the type species) and C. pygmaea, form a basal clade that is sister to the remaining Calibrachoa."

It is puzzling to me why some of these recent phologenetic studies were not adopted in the Jepson Manual (2nd Edition).

Most of the colorful varieties of petunias seen in gardens, flower beds and hanging baskets are hybrids, often listed as Petunia x hybrida. According to Wikipedia (2012) it is thought to be a hybrid between two South American species: P. axillaris (the large white or night-scented petunia) and P. integrifolia (the violet-flowered petunia). Both of these species are cultivated in California gardens, and P. axillaris sometimes occurs as a waif or garden escape that is not truly naturalized.

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