Petunia
Petunia is a genus of about 17 species of annual (rarely perennial) herbaceous plants in the family Solanaceae, native to South America.[1] These plants typically feature sticky-hairy stems and leaves, with flowers that are solitary or in few-flowered cymes, showy, and ranging from white to purple or red in color, with funnelform to salverform corollas measuring 2.5–10 cm long.[1] The fruits are globose to ovoid capsules that dehisce by two valves, containing reniform seeds with a minutely scurfy surface.[1] The genus Petunia is renowned for its horticultural significance, particularly through the interspecific hybrid Petunia × atkinsiana (commonly known as the garden petunia), which originated from crosses between P. axillaris and P. integrifolia and is cultivated worldwide as an ornamental annual.[2] These hybrids exhibit a diverse array of flower colors—including shades of pink, purple, red, white, and even bicolors—and forms, such as grandifloras with large blooms and multifloras with abundant smaller flowers, making them staples in gardens, containers, and hanging baskets.[3] Petunias thrive in full sun and well-drained soil, blooming profusely from spring through fall in temperate climates, though they are tender perennials suited to USDA hardiness zones 10a–11b.[3] In addition to their ornamental value, petunias serve as important model organisms in plant biology research, valued for their large flowers, short generation times, and ease of genetic transformation.[4] Studies on Petunia have advanced understanding of floral development, pigmentation, pollination syndromes, and speciation, with wild species like P. axillaris (white-flowered, night-fragrant, hawkmoth-pollinated) and P. integrifolia (purple-flowered, diurnal, bee-pollinated) providing insights into evolutionary processes.[5] The genus's 17 wild species are primarily distributed in southern South America, particularly Argentina, Brazil, and Uruguay, where they occupy diverse habitats from coastal dunes to inland grasslands.[5]Taxonomy and Description
Classification and Etymology
Petunia is a genus of flowering plants in the family Solanaceae, the nightshade family, which also includes economically important crops such as tobacco, tomatoes, and potatoes. Within Solanaceae, Petunia belongs to the subfamily Petunioideae and the tribe Petunieae. The genus is closely related to Calibrachoa, another group of small-flowered plants that was historically classified under Petunia but distinguished as a separate genus in the late 20th century based on differences in chromosome number, seed morphology, and molecular markers.[6][7][8] The name Petunia derives from the Tupi-Guarani word petun, meaning "tobacco" or referring to an intoxicating plant, which entered European languages via Portuguese and French as pétun. This etymology reflects the indigenous South American recognition of the plant's affinity to tobacco (Nicotiana spp.), another member of the Solanaceae family, due to shared morphological traits like tubular flowers and sticky foliage. The genus was formally described by Antoine Laurent de Jussieu in 1803, drawing on these native names to highlight its New World origins.[9][10] Taxonomic understanding of Petunia has evolved significantly with advances in molecular phylogenetics, particularly in the 2020s. Early classifications recognized around 14-20 species, but recent analyses using high-throughput DNA sequencing have revealed greater diversity, leading to the recognition of additional species and clarification of hybrid origins. A comprehensive 2025 phylogenetic study, incorporating genome skimming data from multiple accessions, produced the first broadly inclusive tree for the genus and proposed revisions to species boundaries based on genetic divergence and evolutionary relationships, recognizing 20 species. Key revisions include recognizing P. axillaris, P. parodii, and P. subandina as independent species; elevating P. integrifolia subsp. depauperata to P. dichotoma; and resurrecting P. guarapuavensis. These updates underscore Petunia's complex speciation in South America, driven by geographic isolation and pollinator specialization.[2][11]Physical Characteristics
Petunia plants are herbaceous, functioning as annuals in temperate regions but as tender perennials in USDA zones 10-11, with growth habits that range from upright and bushy to trailing or cascading. These plants typically reach heights of 15-45 cm, though some varieties extend to 100 cm, featuring branched stems that are viscid-pubescent and often reddish in color.[12][3] The flowers exhibit a characteristic trumpet- or funnel-shaped corolla formed by five fused petals, measuring 5-10 cm across in cultivated forms, with prominent vein patterns that guide pollinators. Colors in wild species are primarily white, pink, or purple, while hybrids display a broader spectrum including red, yellow, and multicolored patterns. The corolla tube is slender and elongated, up to 5 cm long, topped by a limb that expands into the petal lobes, and the calyx is cylindrical with five unequal lobes.[3][13] Leaves are simple, ovate to lanceolate, 2.5-7 cm long and 1-3 cm wide, arranged alternately or oppositely along the stems, and covered in sticky glandular hairs that produce defensive secondary metabolites against herbivores. Stems and leaves share this viscid pubescence, contributing to the plant's overall architecture of spreading lateral branches. The root system is fibrous and shallow, facilitating quick establishment and nutrient uptake in various soils, with adventitious roots common in stem cuttings for propagation.[3][14][15] Wild Petunia species often display more prostrate or scrambling habits with smaller flowers (2-5 cm) and narrower leaves, whereas cultivated hybrids have been bred for compact, mounding forms or vigorous trailing growth exceeding 1 m in length, alongside larger, more vibrant blooms.[16][13]Diversity and Species
Native Species
The genus Petunia encompasses 20 accepted wild species, all endemic to South America, with distributions concentrated in the subtropical and temperate regions of Argentina, Brazil, Uruguay, Paraguay, and Bolivia.[2] These species thrive in diverse habitats such as grasslands, rocky outcrops, and sandy soils, exhibiting variations in flower morphology, color, and pollination strategies that reflect adaptations to local ecosystems. Most species are diploid with a chromosome number of 2n=14, distinguishing the genus from the typical Solanaceae base number of x=12.[17][18][19] Recent phylogenetic analyses as of 2025 reveal two main clades based on corolla tube length—long-tubed (adapted for hawkmoth pollination) and short-tubed (adapted for bee pollination)—originating around 1.5 million years ago during the Pleistocene.[2] The accepted species, as recognized by current taxonomic authorities including a 2025 review, include the following, each with key distinguishing traits and native ranges where noted:[2]- Petunia altiplana T.Ando & Hashim.: A perennial herb with small purple flowers; endemic to high-altitude grasslands in southern Brazil.[20]
- Petunia axillaris (Lam.) Britton, Sterns & Poggenb.: Features large, white, nocturnal, fragrant flowers adapted for hawkmoth pollination; native to southern Brazil, Uruguay, northern Argentina, and Paraguay; chromosome number 2n=14.[21][19]
- Petunia bajeensis T.Ando & Hashim.: Small-flowered with purple corollas; restricted to coastal dunes in southern Brazil.
- Petunia bonjardinensis T.Ando & Hashim.: Compact herb with violet flowers; found in rocky areas of southeastern Brazil.
- Petunia correntina K.V.Kuntz, M.Machado & Stehmann: Recently described species with pale purple flowers; endemic to northeastern Argentina in the Paraná River basin.[22]
- Petunia dichotoma T.Ando & Hashim.: Elevated from subspecies of P. integrifolia; short-tubed purple flowers; southern South America.
- Petunia exserta Stehmann: Distinctive red-orange flowers with exserted stamens for hummingbird pollination; annual or biennial, limited to grasslands in Rio Grande do Sul, Brazil.[23]
- Petunia guarapuavensis T.Ando & Hashim.: Purple-flowered with short corolla tubes; native to inland Paraná state in Brazil; resurrected in recent taxonomy.
- Petunia inflata Fries: White flowers and inflated capsules; distributed in central and northern Argentina, preferring arid rocky habitats; chromosome number 2n=14.[19]
- Petunia integrifolia (Hook.) Schinz & Thell.: Diurnal flowers in shades of red to magenta, bee-pollinated; widespread in southern Brazil, Uruguay, and northeastern Argentina; includes variations in flower sizes; chromosome number 2n=14.[24][19]
- Petunia interior T.Ando & Hashim.: Short-tubed flowers; interior grasslands of Brazil.
- Petunia mantiqueirensis T.Ando & Hashim.: Purple flowers; southeastern Brazil.
- Petunia occidentalis R.E.Fries: Small white to pale purple flowers; ranges from Bolivia to northwestern Argentina in subtropical biomes.[25]
- Petunia parodii Steere: Recognized as independent; white flowers similar to P. axillaris; southern South America.
- Petunia reitzii L.B.Sm. & Downs: Subshrub with lilac flowers; endemic to Santa Catarina state in southern Brazil.[26]
- Petunia saxicola L.B.Sm. & Downs: Rocky habitat specialist; southern Brazil.
- Petunia scheideana L.B.Sm. & Downs: Small purple flowers; coastal Brazil.
- Petunia secreta Stehmann & Semir: Similar to P. axillaris but with smaller, less fragrant white flowers; found in coastal regions of southeastern Brazil.
- Petunia subandina T.Ando & Hashim.: Long-tubed white flowers; Andean-influenced regions in Argentina and Bolivia.
- Petunia toropiensis Stehmann & Larocca: Basal species with purple flowers; known only from a few sites in the Toropi River basin, southern Brazil, and assessed as Critically Endangered due to narrow distribution and habitat loss.[27]