Hydnophytum ferrugineum

Hydnophytum ferrugineum is a epiphyte species of myrmecophytes native to the Cape York Peninsula, Queensland, Australia. It forms a mutualistic relationship with ants on the branches of trees in the tropics. It is distinctive due to the presence of rust-colored hairs covering the bracts near the inflorescences.

Hydnophytum ferrugineum
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Gentianales
Family:	Rubiaceae
Genus:	Hydnophytum
Species:	H. ferrugineum
Binomial name
Hydnophytum ferrugineum P.I.Forst.

Description and biology

Hydnophytum ferrugineum is a subshrub in the genus Hydnophytum, one of two genera of "ant plants" or "ant house plants". It is a member of the family Rubiaceae of angiosperms.

Hydnophytum ferrugineum can grow to be 30 cm (12 in) in diameter and 60 cm (24 in) in height. It has mesomorphic palmately veined glossy leaves arranged oppositely on the stem. The stems are often singular and glabrous. H. ferrugineum has bisexual white flowers with four sympetalous petals in inflorescences at leaf axils. A distinguishing characteristic of this species is long (up to 2 mm (0.079 in)) ferruginous trichomes on the bracts from the inflorescences. There are four anthers located inside the corolla of the flower densely surrounded by trichomes.

Habitat and ecology

Hydnophytum ferrugineum is an epiphyte that lives primarily in moist tropical locations with moderate sun. As an epiphyte, it grows on other plants but is not parasitic on its host plant. Although this species faces little threat, human collecting of ant plants can easily damage local populations. Collecting in this area is common due to rare Orchidaceae species endemic to the region, leading to many people taking samples of H. ferrugineum as well as other ant plants.

Like other species in Hydnophytum, it forms a mutualistic relationship with ants. H. ferrugineum produces a large complex tuber known as a caudex that contains many openings and tunnels throughout. This provides a habitat for ants above the ground and allows them to live in an area they might otherwise not be able to survive in. In addition to the caudex providing habitat for the ants, many species of Hydnophytum also utilize external nectaries to provide ants with a food source. The ants that make their home inside the caudex scavenge food from a wide area and produce waste inside the caudex that then fertilizes the plant. Ants can also help spread pollen or seeds of the plant to reach a wide area. This allows H. ferrugineum to draw resources from a much larger area than would be possible with a root system.

Distribution and history

Hydnophytum ferrugineum is found on the Cape York peninsula of Australia. Cape York has a warm tropical climate throughout the year, providing a warm and wet environment for plants. Although it is only naturally found in this portion of Australia, it has become an increasingly popular houseplant in recent years, often marketed as simply an ant plant or maze plant. H. ferrugineum was first described by Paul Irwin Forster in 2001, given its specific epithet ferrugineum due to the rust-colored hairs located on the bracts.

Phylogeny

Hydnophytum ferrugineum is a generalist, forming mutualistic relationships with many different species of ants, with this characteristic being estimated to be from a common ancestor with ant plant species. This trait likely developed between 15-20 million years ago during the Miocene epoch. Other species (such as some in Hydnophytum or Macaranga) descending from this ancestor later developed specific mutualistic relationships, allowing only one ant species to live inside the caudex by modifying the size of the openings. Others expanded instead, allowing other small animals such as frogs and lizards to make use of the caudex.