2017 ASHS Annual Conference

Poinsettia (Euphorbia pulcherrima) is the most popular holiday potted plant, with eye-catching colorful modified leaves commonly referred to as bracts. Red cultivars are the most abundant, with pink, white, and novelty colors also available. Euphorbia interspecific hybrids between E. pulcherrima and Euphorbia cornastra in vibrant pinks not seen in traditional poinsettias are becoming more popular. Bract color is affected by the location of pigments within the cell layers of the bract tissues. However, the spatial location of pigmented cells in bracts of modern day cultivars of poinsettia bracts has not been examined since 1982, and spatial location in Euphorbia interspecific hybrids has not been reported. The location of pigments in the cell layers of bracts was determined in six modern day poinsettia cultivars (‘Premier Red’, ‘Premier White’, ‘Premier Pink’, ‘Freedom Red’, ‘Polly’s Pink’, and ‘Orange Spice’) and two Euphorbia interspecific hybrids (‘Princettia Dark Pink’ and ‘Luv U Pink’). Cross sections were prepared using polyethylene glycol infiltrated bracts sliced with a thin razor blade. Free-hand thin sections were mounted on a slide and examined under a compound microscope. Pigments were found to be concentrated in the upper and lower epidermis of all cultivars and hybrids examined, with the mesophyll mostly lacking in pigment. Previous reports on the location of pigments in red bracted poinsettias and pink bracted seedlings agree with current findings. However, previous studies reported pigments in only the internal spongy tissues of pink bracted sports while the epidermis appeared colorless. Location of pigments in modern poinsettia cultivars and E. pulcherrima × E. cornastra hybrids is reported for the first time.