Structural Features of Various Trichomes Developed in Salvinia natans

Salvinia natans, an unique water fern having a small rootless body, developed three different types of trichomes throughout the plant. The most peculiar type exhibiting rows of obvious, whitish, multicellular trichome clusters was noticed in the upper surface of the floating leaves. Eight to ten branches within a cluster extended ca. from the leaf surface. No stalk cell was found, however, four large epidermal cells were discernable at the base of four central branches in the cluster. Each branch consisted of obliquely-oriented small cells that gradually decreased in size toward the branch tip. The second type was found in the lower surface of the floating leaves, stems, and sporocarps. Multicellular uniseriate trichomes, ca. long, were distributed all over these structures. The tip of trichome was acicular, but a semi-spheric protuberance of approximately in diameter occurred at the base of each trichome. The protuberance appeared to be firmly attached to the side of the basal cell, however, internal connection to the trichome cell itself was uncertain. The third type was similar to the second in that multicellur uniseriate trichomes with acicular tip and a protuberance at the base were present. However, the trichomes were considerably long relative to the second type, and only occurred along the surface of highly dissected, submerged leaves. A majority of the trichomes exceeded more than 2 mm in length that hung downward in the water. Regardless of trichome type, all trichomes contained a huge central vacuole with very thin cytoplasm, resulting from the fusion of several vacuoles during early trichome development. The various densely-distributed trichomes formed in Salvinia natans probably play an important role in plant buoyancy.