Zinnia is a genus of plants of the tribe Heliantheae within the family Asteraceae. Members of the genus are notable for their solitary long-stemmed 12-petal flowers that come in a variety of bright colors. The genus name honors 18th-century German scientist Johann Gottfried Zinn. The genus is native to scrub and dry grassland in an area stretching from the Southwestern United States to South America, with a centre of diversity in Mexico.
Description Zinnias are annuals, shrubs, and sub-shrubs native primarily to North America, with a few species in South America. Most species have upright stems but some have a lax habit with spreading stems that mound over the surface of the ground. They typically range in height from 10 to 100 cm tall (4" to 40"). The leaves are opposite and usually stalkless (sessile), with a shape ranging from linear to ovate, and a color ranging from pale to medium green. Zinnia's composite flowers consist of ray florets that surround disk florets, which may be a different color than the ray florets and mature from the periphery inward. The flowers have a range of appearances, from a single row of petals to a dome shape. Zinnias may be white, chartreuse, yellow, orange, red, purple, or lilac. Each disc floret has five petals that enclose five stamens bearing anthers. When the petals open, the style elongates and pushes the pollen, produced by the anthers, upward where it becomes accessible to pollinator insects such as hoverflies that eat it. Nectar is secreted at the base of the floret, attracting long‑tongued bees and butterflies. As the style continues to grow, it divides into two branches, with the stigmatic surfaces at the tips maturing to receive pollen.
Etymology The genus name honors the German scientist Johann Gottfried Zinn (1727–1759), who collected Z. elegans seeds in Mexico.
Cultivation Zinnias are easy to grow with potential heavy, brightly colored blooms. Their petals can take different forms as single row with a visible center (single-flowered zinnia), numerous rows with a center that is not visible (double-flowered) and petals that are somewhere in-between with numerous rows but visible centers (semi-double-flowered zinnia). Their flowers can also take several shapes. Zinnias are an annual plant usually grown in situ from seed. They dislike being transplanted due to having a fragile root system, but can be started indoors 4-6 weeks before planting and moved before their roots fully develop. Much like daisies, zinnias prefer to have full sunlight and adequate water. In the preferred conditions they will grow quickly but are sensitive to frost and therefore will die after the first frost of autumn. Zinnias benefit from deadheading to encourage further blooming.
Species Accepted species Zinnia acerosa (syn. pumila) – Arizona, New Mexico, Texas, and Utah in the United States; Coahuila, Durango, Michoacán, Nuevo León, San Luis Potosí, Sonora, and Zacatecas in Mexico. Zinnia americana – Chiapas, Guerrero, Honduras, Jalisco, Michoacán, México State, Nayarit, Nicaragua, Oaxaca, and Veracruz. Zinnia angustifolia – Chihuahua, Durango, Jalisco, San Luis Potosí, and Sinaloa. Zinnia anomala – Texas; Coahuila, and Nuevo León. Zinnia bicolor – Chihuahua, Durango, Guanajuato, Jalisco, Nayarit, and Sinaloa. Zinnia citrea – Chihuahua, Coahuila, and San Luis Potosí. Zinnia coahuilana – Coahuila. Zinnia elegans – from Jalisco to Paraguay; naturalized in parts of United States. Zinnia flavicoma – Guerrero, Jalisco, Michoacán, and Oaxaca. Zinnia grandiflora – Arizona, Colorado, Kansas, New Mexico, Oklahoma, and Texas; Chihuahua, Coahuila, Nuevo León, Sonora, and Tamaulipas. Zinnia guanajuatensis – Northeast Mexico. Zinnia haageana – Guanajuato, Jalisco, México State, Michoacán, and Oaxaca. Zinnia juniperifolia – Coahuila, Nuevo León, and Tamaulipas. Zinnia maritima (syn. palmeri) – Colima, Guerrero, Jalisco, Nayarit, and Sinaloa. Zinnia marylandica – Belize Zinnia microglossa – Guanajuato and Jalisco. Zinnia oligantha – Coahuila. Zinnia peruviana (syn. pauciflora) – widespread from Chihuahua to Paraguay including Galápagos and West Indies; naturalized in parts of China, South Africa, and the United States. Zinnia purpusii – Chiapas, Colima, Guerrero, Jalisco, and Puebla. Zinnia tenella – Durango. Zinnia tenuis – Chihuahua. Zinnia venusta – Guerrero. Zinnia zamudiana – Querétaro, Hidalgo. Zinnia zinnioides – Widespread in Mexico. Formerly included See Glossocardia and Philactis.
Zinnia bidens – Glossocardia bidens Zinnia liebmannii – Philactis zinnioides Zinnia elegans, also known as Zinnia violacea, is the most familiar species, originally from the warm regions of Mexico being a warm–hot climate plant. Its leaves are lance-shaped and sandpapery in texture, and height ranges from 15 cm to 1 meter. Zinnia angustifolia is another Mexican species. It has a low bushy plant habit, linear foliage, and more delicate flowers than Z. elegans – usually single, and in shades of yellow, orange or white. It is also more resistant to powdery mildew than Z. elegans, and hybrids between the two species have been raised which impart this resistance to plants intermediate in appearance between the two. The 'Profusion' cultivars, with both single and double-flowered components, are among the most well-known of this hybrid group. Zinnias are favored by butterflies as well as hummingbirds, and many gardeners add zinnias specifically to attract them.
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