''Christensenia'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...

s in the

botanical Botany, also called plant science, is the branch of natural science and biology studying plants, especially Plant anatomy, their anatomy, Plant taxonomy, taxonomy, and Plant ecology, ecology. A botanist or plant scientist is a scientist who s ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Marattiaceae. The genus is confined to the Indo-Malayan region. The basal chromosome number for this genus is 2n=80. ''Christensenia'' is unique in the Marattiaceae, because of its reticulate venation, palmately arranged leaves and radial synangia. ''Christensenia'' produces enormous amounts of

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

s, up to 7,000 spores per

sporangium A sporangium (from Late Latin, ; : sporangia) is an enclosure in which spores are formed. It can be composed of a unicellular organism, single cell or can be multicellular organism, multicellular. Virtually all plants, fungus, fungi, and many ot ...

. The presence of a radial synangium is an archaic character, very similar to some of the

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

Asterothecaceae/ Psaroniaceae, such as '' Scolecopteris''. ''Christensenia'' itself has no

fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

Species

After the 1993 revision by Rolleri, only two

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

and one variety are recognized: * ''Christensenia aesculifolia'' (Carl Ludwig Blume, Blume) William Ralph Maxon, Maxon (type species) ** ''Christensenia aesculifolia'' var. ''korthalsii'' * ''Christensenia lobbiana'' (Willem Hendrik de Vriese, de Vriese) Rolleri

References

* BRUMMITT, R. K. (1992
Vascular plant families and genera
Royal Botanic Gardens * * Rolleri, C. H. 1993. Revision of the genus ''Christensenia''. Amer. Fern J. 83(1): 3–19. Marattiidae Fern genera {{fern-stub