Monographs Details: Zinnia marylandica D.M.Spooner, Stimart & T.P.Boyle
Authority: Spooner, David M., et al. 1991. Zinnia Marylandica (Asteraceae: Heliantheae), a New Disease-Resistant Ornamental Hybrid. 43: 7-10.
Family:Asteraceae
Description:Species Description - Annual herb. Stems 35-55 cm tall, 0.7-1.3 cm diam, highly branched at base and overall shape of plant hemispherical or urn-shaped, brown to greenish-yellow, pubescent. Leaves sessile to subsessile; blades 5-12 cm long, 1.5-4.5 cm wide, lanceolate to ovate to oblanceolate; scabrous and sessile, glandular ad and abaxially; base cuneate; apex acute to acuminate; margins entire. Capitulescences solitary; peduncles 1-10 cm long, 1-3 mm diam, tomentose. Heads radiate, 15-20 mm long, 40-60 mm diam across extended rays. Involucre campanulate, 9-10 mm long, 18-22 mm diam, phyllaries imbricate, 20-32, 4-seriate, reflexed api- cally, light green to yellow or brown, dark brown and erose at the apex, glabrous to glandular-tomentose; outer phyllaries broadly obovate, 6-8.5 mm long, 5-8 mm wide; inner phyllaries obovate, 10-12 mm long, 4-6 mm wide. Pales conduplicate, 10-14 mm long, 2-2.2 mm wide, stramineous, glabrous except strigose on keel, acute to erose at apex. Ray florets 13-17; pistillate and fertile, persistent on the achenes, ligules creamy white to yellow to red-orange adaxially, greenish- yellow abaxially; 15-28 mm long, 8-15 mm wide; achenes 4-7.5 mm long, 2.5- 3.2 mm wide, oblanceolate, 3-angled, strigose, margins ciliate, tuberculate when mature. Disc florets 120-150, corollas yellow to red-orange, 10-11 mm long, 1- 1.3 mm diam; lobes 2-4.5 mm long, 0.5-0.8 mm wide; achenes 5-7 mm long, 2.8-3.2 mm wide, obovate, laterally flattened, strigose, ciliate at margins, black, brown or black-brown mottled or with whitish longitudinal lines; pappus of 1 or 2 persistent awns to 4.5 mm long.

Discussion:

Plantae inter Z. angustifoliam H.B.K. var. angustifoliam (2n = 22) et Z. violaceam (2n = 24) Cav. hybridae, ut Z. violacea e basi ramosissimae, statura inter parentes intermediae, chromosomatum numerus = 46

TYPE: U.S.A.: Cultivated amphiploid plant grown at the University of Wisconsin-Madison, resulting from crosses between Zinnia angustifolia H.B.K. var. angustifolia and Z. violacea Cav., 28 Aug 1988, Stimart I (HOLOTYPE: WIS; ISOTYPES: MARY, OS).

Early hybridization attempts between Z. angustifolia and Z. violacea utilized an orange-flowered cultivar of Z. angustifolia (Boyle & Stimart, 1982). Interspecific hybrids from these crosses did not express the diversity in ray floret color found among the Z. violacea cultivars used as pollen parents. Instead, hybrids displayed orange, scarlet, or yellow ray florets, i.e., colors more closely resembling the Z. angustifolia parent. A white-flowered cultivar of Z. angustifolia was used in later hybridization attempts and resulted in interspecific hybrids with white,

pink, lavender, salmon, and burgundy ray florets (Boyle & Stimart, 1989), thus considerably broadening the flower color range. Full exploitation of the genetic variability within Z. marylandica by sexual recombination or asexual breeding techniques will probably extend the flower color range beyond that observed to date

Evaluation of Z. marylandica seedlings in greenhouse and outdoor field trials has demonstrated that plants are highly ornamental and prolific in flowering. In addition, the seedlings exhibit high levels of resistance to Alternaria zinniae and Erysiphe cichoracearum and moderate to high levels of resistance to Xanthomonas campestris pv. zinniae (Terry-Lewandowski & Stimart, 1983). Unique combinations of flower color and plant habit have been obtained through interspecific hybridization, and Z. marylandica germplasm provides an expanded gene pool for development of ornamental characteristics not previously found in either parental species.