Diagnostic and microscopical characters of digitalis

 Digitalis, commonly known as foxglove, primarily refers to the dried leaves of Digitalis purpurea or Digitalis lanata. It is used for its cardiotonic properties. Here are the key diagnostic features:

1. Leaves: The leaves are typically lanceolate or ovate, with an acute apex and serrated margin. They can be green to greyish-green.
2. Texture: The leaves are usually coarse, with a hairy surface.
3. Odor: Slight, somewhat unpleasant.
4. Taste: Bitter and acrid.
5. Color: Varies from grey-green to dark green.
6. Venation: Pinnate venation is prominent, with veins branching out and appearing on both the dorsal and ventral surfaces.

Microscopic Characters of Digitalis

To identify digitalis leaves microscopically, some key structures are observed:

1. Epidermis:

   • The upper epidermis has a covering of uniseriate, multicellular, non-glandular trichomes.
   • The lower epidermis also contains glandular trichomes with multicellular heads.
   • Stomata are of the diacytic type (guard cells surrounded by two subsidiary cells perpendicular to the stomatal pore).

2. Mesophyll:

   • The mesophyll is differentiated into palisade and spongy parenchyma.
   • The palisade layer is typically one to two cells thick, located just beneath the upper epidermis.
   • The spongy parenchyma has numerous intercellular spaces, contributing to the plant's leaf texture.

3. Trichomes:

   • The presence of non-glandular trichomes on both surfaces, particularly prominent in Digitalis lanata.
   • Glandular trichomes can be found, which contain essential oils and resins.

4. Calcium Oxalate Crystals:

   • Prismatic or rosette forms of calcium oxalate crystals can be seen, often distributed throughout the leaf tissue.

5. Vascular Bundles:

   • Vascular bundles in the midrib are surrounded by parenchymatous cells, and the xylem and phloem are arranged in a collateral pattern.

6. Sclerenchyma:

   • Sclerenchymatous cells may be found associated with vascular bundles, adding rigidity to the structure.

These microscopical features are crucial in distinguishing Digitalis from other leaves in pharmacognostic examinations.