Unground Alexandria Senna— Inequilaterally lanceolate or lance-ovate leaflets, frequently broken; from 1.5 cm to 3.5 cm in length and from 5 mm to 10 mm in width, unequal at the base, with very short, stout petiolules. The leaflets are acutely cuspidate, entire, brittle, and subcoriaceous, with short and somewhat appressed hairs, few on the upper surface, more numerous on the lower surface, where they occur spreading on the midrib, especially on its lower part. The color is weak yellow to light grayish green to pale olive. The odor is characteristic.

Unground Tinnevelly Senna— Usually unbroken leaflets, from 2 cm to 5 cm in length and from 6 mm to 15 mm in width; acute at the apex; and slightly hairy. The color of the leaves is weak yellow to pale olive.

Histology— Senna shows polygonal epidermal cells with straight walls and frequently containing mucilage; numerous, broadly elliptical stomata mostly from 20 to 35 µm in length, usually bordered by two neighbor-cells with their long axes parallel to that of the stoma, and rarely, though more frequently in Alexandria Senna, a third epidermal cell at the end of the stoma. The hairs are nonglandular, one-celled, conical, often curved, with thick papillose walls, from 100 to 350 µm in length. Palisade cells in a single layer underlie both surfaces except in the midrib region where they occur only beneath the upper epidermis. A meristele occurs in the midrib composed of several radially arranged fibrovascular bundles, the latter separated by narrow vascular rays and supported above and below by arcs of lignified pericyclic fibers. Calcium oxalate occurs in rosette aggregates in the spongy parenchyma and in six- to eight-sided prisms in the crystal fibers, which lie on the outer surface of each group of pericyclic fibers.

Powdered Senna— Dusky greenish yellow to light olive-brown, displaying fragments of veins bearing lignified vessels, tracheids, and crystal fibers, isolated hairs, masses of palisade and spongy parenchyma, fragments of epidermis with stomata, free calcium oxalate rosette aggregates, and prisms from 10 to 20 µm in length. In powdered Alexandria Senna, the hairs are more numerous than in powdered Tinnevelly Senna.

(Official January 1, 2007)