Christensenia aesculifolia

Introduction

Christensenia, with one or two variable species (C. aesculifolia and perhaps C. lobbiana), is confined to tropical forest clearings in the Indo-Malaysian region (Assam, Malacca, Sumatra, Java, Borneo, Sulawesi, Philippines, Solomon Islands).

Vriese and Harting (1853) described four species (as Kaulfussia); in the revision by Rolleri (1993) these were reduced to two species and one variety. Two cytotypes (diploid, n = 40, and tetraploid, n = 80) are known, and their distribution would be of interest (Camus 1990). In the future field studies and molecular evidence will be needed to assess the diversity of this genus. (Christenhusz 2007).

Because of its radial synangia (an archaic character that is also found in fossil Asterothecaceae) Christensenia has been considered to be an ancient lineage, despite the lack of fossil evidence. The reticulate venation, on the other hand, is often considered to be a more derived character, and it has therefore been placed in a family of its own, the Christenseniaceae (Ching 1940). Murdock (2008) showed however that Christensenia is deeply embedded within the Marattiaceae as sister to a clade uniting Marattia s.s. and Angiopteris. The radial synangia and reticulate venation must therefore be derived characters.

Characteristics

Christensenia has creeping, dorsiventral rhizomes, and palmately arranged blades (Rolleri 1993). The pinnae are toothed at the apex, and indeed it resembles a leaf of the horse chestnut (Aesculus hippocastanum). The leaves are thick and leathery and, unlike the other Marattiales, have a reticulate venation. The synangia are radially arranged, a unique character among extant species, but quite common in fossil representatives of the order. The rhizome is stipulate, creeping and usually underground, bearing two rows of fronds, which are otherwise only found in Danaea and "Archangiopteris". Christensenia also has particularly large stomata, which are the largest found in any vascular plant.

Other Names for Christensenia aesculifolia

• Kaulfussia
• Christensenia lobbiana

References

Camus, J. M. (1990). Marattiaceae. In: Kubitzki, K, Kramer, K. U. and Green, P. S. (eds.). The Families and Genera of Vascular Plants, Vol. 1: Pteridophytes and Gymnosperms, pp. 174-180. Springer-Verlag, Berlin, New York.

Ching, R.-C. (1940). Christenseniaceae, a new fern family in tropical Asia. Bull. Fan Mem. Inst. Biol., Bot. 10, pp. 227-229.

Christenhusz, M. J. M. (2007). Evolutionary History and Taxnomy of Neotropical Marattioid Ferns: Studies of an ancient lineage of plants. Annales Universitatis Turkuensis ser. AII, tom. 216, pp. 1-134.

Maxon, W. R. (1905). Christensenia. Proc. Biol. Soc. Wash. 18, pp. 239-240.

Murdock, A. (2008). A taxonomic revision of the eusporangiate fern family Marattiaceae, with description of a new genus Ptisana. Taxon 57, 737-755.

Rolleri, C. H. (1993). Revision of the genus Christensenia. Amer. Fern J. 83, pp. 3-19.

Vriese, W. H. de, and Harting, P. (1853). Monographie des Marattiacées. Arnz, Leiden & Dusseldorf.