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      Species name: Gerbera hybrida
      Overview
    Gerbera botany, taxonomy and distribution
    The genus Gerbera is comprised of 29 species distributed in the Americas from Mexico to South America, Asia from Yemen and countries east of and including the Himalayan plateau to Bali and Africa including sub-Saharan Africa and Madagascar (Baird et al. 2010). Dispersal-variance analyses indicate South America as the ancestral area of the Gerbera-complex, consistent with the hypothesis that the basal clades of the Asteraceae arose in South America (Panero and Funk, 2008). Taxonomically, Gerbera is placed in the Mutisioideae, the fourth-most diverse Compositae subfamily. Commercially, Gerberas are propagated vegetatively and sold as a cut-flowers. Gerbera hybrida is a man-made hybrid most likely between G. jamesonii Bolus ex Hook. f. and G. viridfolia Shultz-Bip (Bremer, 1994; Hansen, 1999).
    Flowers in the Compositate (Asteraceae) family are composed of morphologically different types of flowers and Gerbera (Gerbera hybrida) displays most of the features common to this family. Each Gerbera flower possesses three different types of flowers; an outer ring of ray florets, a middle ring of trans florets, and an inner ring of disk florets (Figure 1). The ray and disc flowers are packed tightly into a flower head called the capitulum. The marginal ray flowers are strongly ligulate and zygomorphic with fused showy petals; the female ray flowers have anthers that are initiated but aborted later in development; and the centrally-located disc flowers contain both anthers and carpels. The trans flower in Gerbera are female, like the ray flowers, but the length of the petals vary among varieties. Gerbera flowers also possess hair-like structures, called pappus. Evidence that these structures are modified sepals comes from experiments that show flower-organ determination may be modified with MADS-box genes. The stamens of Gerbera flowers are aborted in marginal flowers, the petals and anthers are fused into tubular structures and the plant possesses inferior ovaries. Early in development, the three main flower types (ray, trans and disk) are morphologically similar. Morphological differentiation of flower types occurs through the action of the TCP transcription factors on CYCLOIDEA-like TCP protein domains.

    Gerbera genetics
    Gerbera hybrida is a diploid plant with a 2C DNA value estimated at 5.1 pg (about 5.0 Gb), slightly smaller than lettuce (Lactuca sativa; 5.5 pg, 5.4 Gb) and maize (Zea mays, 5.4 pg, 5.3 Gb; Bennett and Leitch, 1997; Kew database). In the floral trade, Gerbera daisies are classified and sold as either single-flowered, crested or spider cultivars, each typified by characteristic enlarged or diminished ray, trans or disk flowers (Figure 2). Three alleles (Crd, Cr, Sp) with incomplete dominance largely control the floral types among the Gerbera cultivars and a single dominant gene (Dc) controls disk color (Kloos et al. 2004; 2005).

    Gerbera economic use
    Gerbera is the fifth-most used cut flower worldwide and is an important model species for studies of flower development. In addition to Gerbera daisies, the Composites include many ornamental species of significant commercial value. These include Osteospermum (Osteospermum spp), calendula (Calendula officinalis L.), black eyed Susans (Rudbeckia hirta L.), marigolds (Tagetes patula L. and Tagetes erecta L.), various chrysanthemum species, and cone flowers (Echinacea spp). Each of these ornamental species has floral morphology similar to Gerbera daisies. The genomic information generated from sequencing the gene space of Gerbera will benefit the improvement of other floriculture crops within the Compositae and serve as a model of flower development.

      Resources
      Images of Gerbera hybrida
      
      Figure 1: Gerbera hybrida flowers are a composite of three flower types, the outer ray florets, middle trans florets, and the inner disk florets. This pattern is common to many Compositae floral crops.
    Photo credit: Brian Johnston (microscopy-UK)
      
      Figure 2: Single, double and spider Gerbera hybrida flowers. (photo by D.W. Still)
      CGP Activities
    Reduced-representation libraries of Gerbera hybrida 'Terra Regina' and its wild progenitor Gerbera jamesonii have been sequenced using Illumina GA II and HiSeq. After filtering, a total of 76,778,000 and 77,427,000 reads for G. jamesonii and G. hybrida 'Terra Regina', respectively, have been obtained. Assembly is in progress in the Still lab. Additional Gerbera hybrida cultivars or species will be sequenced. These data will provide a useful resource for floral development studies and will be a significant resource for commercial breeders.
      Publications
    Baird, K.E., Funk, V.A., Wen, J., and A. Weeks. 2010. Molecular phylogenetic analysis of Leibnitzia Cass. (Asteraceae: Mutisieae: Gerbera-complex), and Asian-North American disjunct genus. J Systematics Evol. 48: 161-174.

    Bennett, M. D. and I.J. Leitch. 1997. Nuclear DNA amounts in Angiosperms--583 new estimates. 10.1006/anbo.1997.0415. Annals Bot. 80: 169-196.

    Bremer, K. 1994. Asteraceae: Cladistics and Classification. Timber Press, Portland, Oregon.

    Hansen, H. van. 1999 A story of the cultivated Gerbera. The New Plantsman 6:85-95.

    Kloos, W.E., George, C.G., and L. K. Sorge. 2004. Inheritance of the flower types of Gerbera hybrida. J Amer Soc Hort Sci 129:802-810.

    Kloos, W.E., George, C.G., and L. K. Sorge. 2005. Dark disc color in the flower Gerbera hybrida is determined by a dominant gene, Dc. HortScience 40: 1992-1994.

    Panero, J. L., and V. A. Funk. 2008. The value of sampling anomalous taxa in phylogenetic studies: major clades of the Asteraceae revealed. Mol. Phylogenet. Evol. 47: 757-782.

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