''Christensenia'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes exce ...

s in the

botanical Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Ancient Greek wo ...

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Marattiaceae Marattiaceae is the only family of extant (living) ferns in the order Marattiales. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), Marattiales is the only order in the subclass Marattiidae. The family has six genera and about ...

. The genus is confined to the Indo-Malayan region. The basal chromosome number for this genus is 2n=80. ''Christensenia'' is unique in the

, because of its reticulate venation, palmately arranged leaves and radial

synangia A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cy ...

. ''Christensenia'' produces enormous amounts of spores, up to 7,000 spores per sporangium. The presence of a radial

synangium A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cy ...

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 preserved ...

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 In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

and one

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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