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The anatomy of involucral bracts (IB) of the capitulum was studied in two sunflower domesticated primitive genotypes ( Helianthus annuus  L.), Havasupai and Hopi, HA89B line and DKOP3845 hybrid. Stomata and trichomes were counted on the adaxial and abaxial epidermis. In all cases the IB showed an one-layered adaxial and abaxial epidermis, secretory ducts and parenchymatic cells with abundant chloroplast. The vascular system was similar to that of the foliage leaves; however, their bundles were smaller, with an abaxial surface with higher abundance of glandular and non-glandular trichomes and with the presence of stomatas. IB of Havasupai and Hopi showed higher number of adaxial hypodermic strata than those of HA89B and DKOP3845 (4 vs. 1) and one mesophyllum with inverted polarity with respect to a foliage leaf: the presence of a spongy parenchyma on the adaxial side was observed with a rudimentary palisade parenchyma on the abaxial side. Stomatal density of the IB was significantly higher in Hopi and Havasupai than in HA89B and DKOP3845, with values ranging from 132 to 156 vs. 73 to 110 stomata/mm 2  respectively. It is concluded that from the functional point of view, sunflower breeding produced undesired changes in the IB anatomy.

Involucral Bracts Anatomy in the Capitulum of Primitive Strains and Modern Genotypes of Sunflower ( Helianthus annuus L.)