The Truth behind the Confusion: the Identity of Java Moss and other tropical aquarium mosses

B.C. Tan 1 and Loh Kwek Leong 2 Photographers: C. King Hshiau Horng 1 , Lim Yao-Hui 1 and Chua Keng-Soon 1

1) Department of Biological Sciences, National University of Singapore, Singapore 119260 2) "", Singapore

In a recent article in Aquatic Gardener (vol. 18 (1): pp. 36-39, 2005), it was reported that the aquarium hobbyists in Singapore are spoiled in having many kinds of "aquatic" mosses available for planting in fish tanks. Nonetheless, there is difficulty encountered in recognizing correctly these different aquarium mosses available to the hobbyists and the growers. Indeed, in Singapore, we have seen several plant samples traded under the same common name, but have proven to be of different moss species when examined under the microscope.

Aquarium mosses, and for that matter, aquatic plants in general, readily change their form, branching pattern and leaf shape when growing in water. Aquarium plant enthusiasts know from experience that the emersed and submersed forms of the same plant species, e.g. Myriophyllum sp. (milfoil), can look different depending on the water and light factors. It would seem therefore that for an accurate identification of the species, one will have to depend on the less changeable plant characters, such as the leaf cell morphology and the reproductive structures, as in the case of mosses.

The following discussion of morphological differences seen among aquarium mosses grown in Singapore is based on an article published in 2004 in Singapore Scientist (102: 8-11) prepared by the same authors. To help the readers identify the plant specimen, photos of microscopic features of individual aquarium moss species are reproduced here to serve as pictorial guides. Readers are referred to Loh (2005), for photos of the plant habit of various aquarium mosses reported in this article.

Although widely grown as ornamental "aquatic plants" in aquaria these days, many of the so-called aquarium mosses, except for the Java Moss and the Willow Moss, are not aquatic in their natural habitat.

Java Moss is, no doubt, the most popular aquarium moss known in the world today. Its true identity has been identified as Taxiphyllum barbieri (Card. & Coppey) Iwats. by Prof. Z. Iwatsuki (1982) and discussed further in another publication (Takaki et al.,1982). In spite of the two clarifications made in 1982, the scientific name of Java Moss has continued to be quoted erroneously as "Vesicularia dubyana" in recent references and handbooks of aquarium plants. Vesicularia dubyana is a different moss species, the so-called Singapore Moss.

Java Moss can be readily recognized by the presence of many long branches with short to long, distantly spaced, lateral branchlets. The small, flattened leaves are arranged on two sides of the stem and branches. When tied to driftwood or rocks, the long branches of the plant become more profusely produced. Observed under the microscope, the leaf shape is oblong to oblong-lanceolate, with a short and wide leaf tip. Its leaf cells are long and narrow, with thin- to moderately thick walls. The leaf margins are toothed throughout. Two short "veins" (or costae) can be clearly seen at the base of the leaf blade.

Interestingly, the species, since its first description, has not been seen to produce fruiting capsules in cultivation. Often time, alleged specimens of Java Moss with capsules that were sent to us for confirmation turned out to be of a different moss species that grows in mixture with the Java Moss.

A rising star among the tropical aquarium mosses lately is the Christmas Moss (Vesicularia montagnei (Bel.) Broth.). The plant got its common name because the mature fronds hang down and overlap each other like the branches of a Christmas tree. Many hobbyists grow them as a moss wall, decorating the aquascape of fish tank.

Grown submersed, the moss can produce long triangular fronds. Its more or less regularly pinnate to subpinnate branches are characteristic. The leaves are nearly round to broadly oval with an abruptly short and sharp apex, and the leaf cells are broad and short in outline, and with thin walls. The two leaf costae are also somewhat conspicuous. In its natural environment, Christmas Moss grows on shaded wet bank of stream and creeks, and also on wet shaded ground in forest. It is a widespread species in tropical Asia.

Another related aquarium moss that has gained popularity these days is the Erect Moss (Vesicularia reticulata (Dozy & Molk.) Broth.). The plants prefer high lighting when grown in water. The common trade name describes the upward orientation of its stems and branches when grown submersed. The leaves are ovate to ovate-lanceolate with consistently long and stout acuminate tip. The leaf cells are oblong to short elongate and broad, longer than those seen in Christmas Moss, but not as long and narrow as the leaf cells of Java Moss. Like Christmas Moss, Erect Moss is also a widespread, terrestrial moss species in tropical Asia that colonizes wet habitats.

Among the local aquarium mosses, the Singapore Moss (Vesicularia dubyana (C. Muell.) Broth.) is the most variable in form. It is a widespread species in many parts of Asia forming large mats on wet soil in shaded places. In the aquarium, the plants look like the Christmas Moss except that their fronds are shorter and not so triangular in outline. The similarity in appearance between these two mosses has given rise to the belief among hobbyists that there are two types of Christmas Moss, one with big fronds, and the other with small ones (referring to the Singapore Moss).

Typical plant of Singapore Moss has an irregularly pinnate branching pattern. Its leaves are rather variable in shape, ranging from oblong to lanceolate, and with short or long leaf apex. Because of its capability to assume many forms in fish tanks, the correct identity of Singapore Moss is best done by a microscopic examination of the distinguishing leaf cell characters. The leaf cells of Singapore Moss are somewhat oblong and broad, and with moderately thick walls, like that of Erect Moss.

One recently introduced and rather pricey aquarium moss is the Taiwan Moss [cf. Taxiphyllum alternans (Card.) Iwats.]. As the common trade name suggests, it is exported from Taiwan but we can not be sure if the plants truly originated from the island country. The fronds of Taiwan Moss exhibit a triangular shape somewhat similar to the Christmas Moss, but are distinctively more equilateral. The ends of the branches curl up slightly when grown in water. Unlike the Christmas Moss which feels hard when touched, the Taiwan Moss has a soft texture and looks delicate when grown in a bunch.

Like Java Moss, the leaves of Taiwan Moss are oblong-lanceolate with two well marked costae, but have a gradually (not abruptly) longer and sharper apex. Its leaf cells, like those of Java Moss and other species belonging to the same genus (Taxiphyllum), are narrow and long. However, a distinct difference between these two species can be observed in their leaf margins. In Taiwan Moss, only the upper leaf apex is irregularly and minutely toothed. In contrast, the leaf margins of Java Moss are toothed throughout.

Another recently introduced aquarium moss allegedly from mainland China is the Weeping Moss [cf. Vesicularia ferriei (Card. & Thér.) Broth.).]. The mature fronds of this moss droop like the branches of a weeping willow tree. The overall leaf shape and the oblong and broad leaf cells approach that of Christmas Moss, but the leaf is without an abruptly short and sharp apex. This aquarium moss still needs time to gain popularity among the aquarium plant enthusiasts in Singapore.
References - Iwatsuki, Z. 1982. A new combination of an Asiatic species in Taxiphyllum. Miscellanea Bryologica et Lichenologica 9: 115. Loh, K.L. 2005. The lowdown on aquatic mosses. The Aquatic Gardener 18 (1): 36-39. Takaki, N., R. Watanabe, and Z. Iwatsuki. 1982. Bryophytes in aquariums for tropical fish. Proceedings of the Bryological Society of Japan 3(5): 65-68 (in Japanese). Tan, B.C., K.-L. Loh and C.-W. Gan. 2004. What is the true identity of Java Moss and other aquarium mosses sold in Singapore shops? Singapore Scientist 102: 8-11.