|photos copyright B.-Y. Sun|
Mankyua chejuense is a recently discovered genus and species found in a lowland swampy area on Cheju Island, off the southern coast of the Korean Peninsula (Sun et al., 2001). Its affinities with the Ophioglossaceae are fairly clear. Mankyua possesses a fertile spike (sporophore) originating dorsiventrally from the adaxial side of the vegetative trophophore, eusporangiate sporangia without annuli, and noncircinate leaf vernation. These three characters, especially the first, place it in the Ophioglossaceae. Also, recent DNA analyses confirm the placement of Mankyua in Ophioglossaceae (Sun, 2002).
At first glance, Mankyua looks almost like a fake plant that a herbarium worker with too much time put together from fragments of representatives of other Ophioglossaceae genera. The intriguing combination of morphological character states represented in Mankyua have some implications for Ophioglossaceae systematics, and possibly understanding character evolution in the family, at least based upon extant representatives.
As Mankyua has a mixture of character states that were previosuly thought of as distinctive for other genera in the family, I present a morphological description of Mankyua organized so that the similarity to other genera is explicit. Character states presented below are taken from the description of Mankyua in Sun et al.(2001). I have listed baculate spore ornamentation as an additional character state shared by Mankyua and Helminthostachys not identified by Sun et al. (2001). Also, Sun et al. (2001) state that Ophioglossum s.l. have simple (unbranched) sporophores, but at least one species (O. pendulum) sometimes has compound sporophores.
Mankyua is a distinct genus in Ophioglossaceae because of its unique combination of character states. The presence of an Ophioglossum type of sporophore on a plant with the habit and leaf organization of Helminthostachys represents something similar to what the possible ancestor of the ophioglossoid lineage may have been. Currently, molecular data support two lineages within Ophioglossaceae; a botrychioid lineage with Helminthostachys as the basal group and Botrychium s.l. as derived, and an ophioglossoid lineage constisting of Ophioglossum s.l. (Hauk, 2000). In informal discussions, Hauk and I postulated that the ancestor of the ophioglossoid lineage would possibly have compound leaves, as in Helminthostachys, but would possess an Ophioglossum type of sporophore, i.e. sunken sporangia on a simple or compound spike-like structure. Mankyua seems to morphologically fill this role, and could be an extant representative of this ancestral lineage.
Recent molecular data presented by Sun (2002) places Mankyua with the botrychioid lineage. However, Sun (2002) did not provide enough information in this publication to understand where Mankyua is located within the lineage, and thus it is not possible to use this information to examine morphological evolution. But I would imagine that Mankyua came out as either basal in the botrychioid lineage, or just above Helminthostachys in such an analysis. If the former is accurate, then the evolution of the typical botrychioid branched sporophore with exposed sporangia would have probably evolved once in the family, and the sunken sporangia of Mankyua could represent a primitive state for this character. However,if Mankyua is placed above Helminthostachys in such an analysis, then the sporophore may be a more variable character in the family than our extant taxa demonstrate. It would suggest that exposed and sunken sporangia may have evolved more than once, and that this character would be more evolutionary plastic than previously thought. We shall have to wait and see a full presentation of the data analyses to see what implications Mankyua has for morphological evolution in Ophioglossaceae.
Mankyua's existence does destroy anyone's ambitions to separate Ophioglossaceae into two families. Many authors, especially in Asia, recognize the Botrychiaceae and Ophioglossaceae. I think that the discovery of Mankyua unites the family. The mixture of character states presents in Mankyua combines the distinguishing states for each family, and thus abolishes the taxonomic boundaries between the two segregate families. Also, the interesting character states in Mankyua suggests that we may not understand the plasticity of character states in Ophioglossaceae, and until further research is done on the genus we will still be in the dark about its implications for morphological evolution and systematics.
Hauk, W.D. 2000. Phylogeny of the Ophioglossaceae based on molecular and morphological characters. Amer. J. Bot. (abstracts) 87(6): 90.
Sun, B.-Y., M.H. Kim, C.H. Kim, and C.-W. Park. 2001. Mankyua (Ophioglossaceae): a new fern genus from Cheju Island, Korea. Taxon 50: 1019-1024.
Sun, B.-Y. 2002. Characteristics of fern flora of Korea with emphasis on the endemic genus Mankyua (Ophioglossaceae) from Cheju Island, Korea. First Korean Academy of Science and Technology / Hungary Academy of Science Bilateral Symposium Proceedings 1: 62-68.
Tryon, A. F. and B. Lugardon. 1991. Spores of the pteridophyta: Surface, wall structure, and diversity based on electron microscope studies. Springer-Verlag, New York.