Aloe and Senna are two important medicinal plants known for their distinct diagnostic features, which are often used in pharmacognosy to identify raw drug materials. Here are the key diagnostic features of each:

Study of medicinal plants

Aloe

  1. Leaf Characteristics:

    • Aloe vera has fleshy, thick, and succulent leaves that are lanceolate in shape.
    • The leaves are typically green, with a waxy, smooth surface that can sometimes have white spots in young plants.
    • The margins of the leaves are serrated, with small white teeth.

  2. Transverse Section (T.S.):

    • The transverse section of the aloe leaf shows a distinct three-layered structure:
      • Cuticle: A thick layer that protects against water loss.
      • Epidermis: Covered with a thick cuticle.
      • Parenchyma Cells: The central part contains parenchyma cells filled with mucilage, also known as aloe gel.

  3. Internal Structures:

    • Aloe Juice: The juice, or latex, is located just beneath the outer green rind of the leaf. This yellowish latex contains anthraquinones (e.g., aloin), which are responsible for aloe's laxative effect.
    • Vascular Bundles: Scattered throughout the parenchyma tissue, forming an irregular pattern.

  4. Microscopical Features:

    • The presence of needle-shaped calcium oxalate crystals.
    • The mucilage cells are also an identifying feature.

Senna

  1. Leaf Characteristics:

    • Senna consists of dried leaflets, usually from Cassia angustifolia or Cassia acutifolia.
    • The leaflets are oblong-lanceolate, with an entire margin, and are pale green in color.
    • They are pinnate with 4-5 pairs of leaflets attached oppositely.

  2. Microscopical Features:

    • Epidermal Cells: Senna leaflets show polygonal epidermal cells.
    • Trichomes: Both glandular and non-glandular trichomes are present. Non-glandular trichomes are unicellular, while glandular trichomes are typically stalked.
    • Calcium Oxalate Crystals: Prism-shaped crystals are often seen in the mesophyll.

  3. Transverse Section (T.S.):

    • The T.S. of the senna leaflet shows a dorsiventral arrangement, with a clear distinction between palisade and spongy parenchyma.
    • Palisade Cells: Present just below the upper epidermis, forming 1-2 layers.
    • Vascular Bundles: These are collateral and covered by bundle sheath cells.

  4. Chemical Tests:

    • Senna contains sennosides, which are responsible for its laxative action. The presence of sennosides can be confirmed by Bornträger's test, which gives a pink to red color upon reaction, indicating the presence of anthraquinone derivatives.

Summary

  • Aloe is characterized by its thick, succulent leaves with serrated margins, parenchyma with mucilage, and the presence of aloin.
  • Senna features pinnate, oblong leaflets with specific trichomes and sennosides as the active chemical constituents.

These diagnostic features help distinguish aloe and senna in botanical and pharmacognostic studies, particularly when used as crude drugs.