Helianthus leaf, LM

Helianthus leaf. Light micrograph (LM) of a transverse section through the leaf (pinna) of a helianthus (sunflower). Helianthus (sunflower) is a genus comprising about 70 species of annual and perennial flowering plants in the daisy family Asteraceae. Except for three South American species, the species of Helianthus are native to North America and Central America. Present are several central vascular bundles made up of phloem sieve cells (blue) and xylem tracheids (red). Dicot leaves are dorsoventral as the upper and lower surfaces of the leaves are distinguished. The vascular bundle is large in dicot leaf whereas in monocot leaf, both small and large parallel vascular bundles are present. Magnification: x20 when printed at 10 centimetres wide, Photo by STEVE GSCHMEISSNER/SCIENCE PHOTO LIBRARY