''Adiantum vivesii'' is a rare

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 ...

maidenhair fern ''Adiantum'' (), the maidenhair fern, is a genus of about 250 species of ferns in the subfamily Vittarioideae of the family Pteridaceae, though some researchers place it in its own family, Adiantaceae. The genus name comes from Greek, meaning "un ...

known by the common name Puerto Rico maidenhair.

Distribution

''Adiantum vivesii'' is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and Unincorporated ...

, where it is known from a single population made up of perhaps 1000 individuals near Quebradillas, in the San Juan – Caguas – Guaynabo metropolitan area on the northern side of the island.''Adiantum vivesii'': Five Year Review.
USFWS. The fern was discovered in 1985 and described to science as a new species in 1989.Proctor, G. R. (1989). Ferns of Puerto Rico and the Virgin Islands. ''Mem. New York Bot. Gard.'' 53:1-389 Soon after, it was listed as an

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...

. It is a putative hybrid between ''Adiantum obliquum'' and ''A. tetraphyllum''. In 2003 a specimen that most likely represents this species was collected on Petit Morne in Martinique by botanist

Maarten Christenhusz Dr Maarten Joost Maria Christenhusz (born 27 April 1976) is a Dutch botanist, natural historian and photographer. Career He was born in Enschede, the Netherlands, received his undergraduate and master's degrees from Utrecht University in Bi ...

collection number 2678 (BM, SP, TUR, U, UC), which means that the hybrid has occurred twice independently.

Single population — sterile hybrid

In 2000, a student at the

University of Puerto Rico The University of Puerto Rico ( es, Universidad de Puerto Rico, UPR) is the main public university system in the U.S. Commonwealth of Puerto Rico. It is a government-owned corporation with 11 campuses and approximately 58,000 students and 5,3 ...

published a

master's thesis A thesis ( : theses), or dissertation (abbreviated diss.), is a document submitted in support of candidature for an academic degree or professional qualification presenting the author's research and findings.International Standard ISO 7144: ...

detailing her studies of the rare fern. She had carefully dug around most of the single population and discovered it was actually one individual connected by a long

rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...

. The fern produces

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

s but no

gametophyte A gametophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has on ...

s and there were no new, small individuals in the vicinity; the student concluded that the fern does not undergo

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

, only

vegetative reproduction Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or spec ...

, sprouting up from its extensive rhizome. Evidence supports the conclusion that the fern is one plant that is a

sterile hybrid In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents (such as in ...

of two common fern species, and as it does not reproduce but only increases in size by resprouting, it is not a valid

in its own right. Therefore, the

United States Fish and Wildlife Service The United States Fish and Wildlife Service (USFWS or FWS) is an agency within the United States Department of the Interior dedicated to the management of fish, wildlife, and natural habitats. The mission of the agency is "working with othe ...

recommends it be removed from the

endangered species list On 29 January 2010, the IUCN Red List of Threatened Species identified 5220 (2754 animals, 1 fungus, 2464 plant, 1 protist) endangered species, subspecies and varieties, stocks and sub-populations. For IUCN lists of endangered species by kingdom, ...

.Fish and Wildlife Service recommends change in the Endangered Species Act Status for Caribbean fern.
Press Release August 19, 2008. As of 2011 it is still on the list.

References

vivesii Ferns of the Americas Endemic flora of Puerto Rico Ferns of the United States Plants described in 1989 Endangered flora of the United States {{Pteridaceae-stub