In this article we will discuss about the morphology of porella with the help of a suitable diagram.
A large and more specialized genus of Jungermanniales, Porella, is distributed all over the world, except Arctic and Antarctic regions. About 34 species have been recorded from India; mainly from Himalayas where it grows luxuriantly. The genus is relatively rare in the hills of south India.
The plant forms dense cushions on moist rocks or grows as epiphyte on the bark of trees, especially at the base. Rarely, the plant can be seen growing on soil. P. platyphylla is a cosmopolitan species; it occurs in Asia, Europe and North America.
The plant body is a dorsiventral leafy axis (Fig. 2.11 A), attached to the substratum by rhizoids arising from the ventral surface. The prostrate axis is bi- or tri-pinnately branched. The secondary branches grow somewhat erect and have scant or no rhizoids. On the axis are three rows of leaves (Fig. 2.11B); two lateral and one ventral. The lateral leaves are complicate bipartite, divided into two lobes; a bigger dorsal lobe and a smaller ventral lobe, the lobule.
The dorsal lobes are incubously arranged (the anterior margin of a leaf lobe covers the posterior edge of leaf lobe in front of it). The leaf is attached to the stem transversely or is decurrent, its margin is variable; entire in P. acutiphylla or toothed in P. denticulata, the apex is acute or round.
The lobules are parallel to the axis in a row on either side and are similar in morphology to the lobes. The leaves on ventral surface, amphigastria, are larger than lobules but similar to lobules in shape.
The leaves with their lobes form an excellent system for absorption and retention of moisture. Rhizoids are basically anchoring structures.
The growth is due to an apical cell with three cutting faces; two dorsolateral and one ventral.
Branching of stem is monopodial. A branch originates from lower half of a lateral segment. As a result, the branch replaces the ventral lobe of a dorsal leaf or in other words the leaf subtending a branch has no lobule.
Internally, the stem consists of a thick-walled cortex of 2-5 layers and it encloses a thin-walled portion of elongated cells, the medulla. The leaves are uni-stratose, single layer of chlorophyllous cells, with uniform oil bodies. In most of species the leaf cells are thickened at the corners forming trigones.
