''Rhinanthus osiliensis'', in English known by the common name Saaremaa yellow rattle, is a

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

in the genus ''

Rhinanthus ''Rhinanthus'' is a genus of annual parasitic plant, hemiparasitic herbaceous plants in the family Orobanchaceae, formerly classified in the family Scrophulariaceae. Its species are commonly known as rattles. The genus consists of about 30 to 40 ...

'' in the

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 ...

Orobanchaceae Orobanchaceae, the broomrapes, is a family (biology), family of mostly parasitic plants of the order (biology), order Lamiales, with about 90 genus, genera and more than 2000 species. Many of these genera (e.g., ''Pedicularis'', ''Rhinanthus'', ...

. It is

endemic Endemism is the state of a species being found only 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 foun ...

to the Estonian island

Saaremaa Saaremaa (; ) is the largest and most populous island in Estonia. Measuring , its population is 31,435 (as of January 2020). The main island of the West Estonian archipelago (Moonsund archipelago), it is located in the Baltic Sea, south of Hi ...

in the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...

. Plants growing on the Swedish island

Gotland Gotland (; ; ''Gutland'' in Gutnish), also historically spelled Gottland or Gothland (), is Sweden's largest island. It is also a Provinces of Sweden, province/Counties of Sweden, county (Swedish län), Municipalities of Sweden, municipality, a ...

have been ascribed to ''R. osiliensis'', too, but genetic analyses have not supported this hypothesis. Morphological features of ''R. osiliensis'' include glandular hairs on the sepals (calyx) and relatively narrow leaves. It is a late-flowering species of ''Rhinanthus'', flowering from the end of July onwards.

Habitat, distribution, and ecology

''Rhinanthus osiliensis'' is strictly

to the western part of

island, Estonia, with a highly restricted geographic range. The species is a habitat specialist that primarily inhabits

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime (mineral), lime or being chalky. The term is used in a wide variety of Science, scientific disciplines. In zoology ''Calcare ...

spring

fen A fen is a type of peat-accumulating wetland fed by mineral-rich ground or surface water. It is one of the main types of wetland along with marshes, swamps, and bogs. Bogs and fens, both peat-forming ecosystems, are also known as mires ...

s, which are naturally scarce

wetland A wetland is a distinct semi-aquatic ecosystem whose groundcovers are flooded or saturated in water, either permanently, for years or decades, or only seasonally. Flooding results in oxygen-poor ( anoxic) processes taking place, especially ...

habitats. It also occurs in other wetland environments such as species-rich fens and paludified meadows. The plant can temporarily colonize marginal habitats like ditch verges and

stream bank In geography, a bank is the land alongside a body of water. Different structures are referred to as ''banks'' in different fields of geography. In limnology (the study of inland waters), a stream bank or river bank is the terrain alongsid ...

s, though such populations tend to be transient. As an annual

hemiparasitic A parasitic plant is a plant that derives some or all of its nutritional requirements from another living plant. They make up about 1% of angiosperms and are found in almost every biome. All parasitic plants develop a specialized organ called the ...

plant, ''R. osiliensis'' attaches to and derives nutrients from the roots of perennial herbaceous

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

plants. The species typically begins flowering in the second half of July and early August, with

pollination Pollination is the transfer of pollen from an anther of a plant to the stigma (botany), stigma of a plant, later enabling fertilisation and the production of seeds. Pollinating agents can be animals such as insects, for example bees, beetles or bu ...

carried out by insects, particularly

bumblebee A bumblebee (or bumble bee, bumble-bee, or humble-bee) is any of over 250 species in the genus ''Bombus'', part of Apidae, one of the bee families. This genus is the only Extant taxon, extant group in the tribe Bombini, though a few extinct r ...

s. Its seeds, which ripen by late September or early October, are relatively large and heavy, lacking an active dispersal mechanism. Consequently, most offspring are found in close proximity to the parent plant. The seeds generally maintain viability for only one year, and the species does not form a persistent

seed bank A seed bank (also seed banks, seeds bank or seed vault) stores seeds to preserve genetic diversity; hence it is a type of gene bank. There are many reasons to store seeds. One is to preserve the genes that plant breeders need to increase yield, ...

. The population of ''R. osiliensis'' was estimated at about 26,000–32,000 individuals as of 2010, distributed across several dozen established populations. Many of these populations are located within

nature reserve A nature reserve (also known as a wildlife refuge, wildlife sanctuary, biosphere reserve or bioreserve, natural or nature preserve, or nature conservation area) is a protected area of importance for flora, fauna, funga, or features of geologic ...

s. The species faces significant habitat challenges, as spring fens have lost about two-thirds of their total cover since the 1950s due to drainage activities. Also, the surrounding landscape has undergone considerable change, with a substantial increase in

forest cover Forest cover is the amount of trees that covers a particular area of land. It may be measured as relative (in percent) or absolute (in square kilometres/ square miles). Nearly a third of the world's land surface is covered with forest, with clos ...

that may impede

gene flow In population genetics, gene flow (also known as migration and allele flow) is the transfer of genetic variation, genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent ...

between populations by hindering the movement of pollinators. Research has shown that ''R. osiliensis'' populations show relatively high levels of

inbreeding Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely genetic distance, related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genet ...

and have experienced

genetic bottleneck A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities such as genocide, speciocide, wid ...

s, likely resulting from

habitat loss Habitat destruction (also termed habitat loss or habitat reduction) occurs when a natural habitat is no longer able to support its native species. The organisms once living there have either moved elsewhere, or are dead, leading to a decrease ...

and fragmentation. The species' short life cycle and specific habitat requirements make it particularly vulnerable to landscape changes, with both the loss of suitable wetland habitats and the increase in forest cover posing serious threats to its long-term persistence.

References

{{Authority control Parasitic plants

Rhinanthus minor ''Rhinanthus minor'', known as yellow rattle, is a herbaceous wildflower in the genus ''Rhinanthus'' in the family (biology), family Orobanchaceae (the broomrapes). It has circumpolar distribution in Europe, Russia, western Asia, and northern No ...

osiliensis