Nematanthus is a genus containing approximately 30 species found in the montane forests of southeastern Brazil. Most of the nematanthus species have a trailing or bushy growth habit that grow well in hanging baskets. Their vigorous growth rate, unique blossoms, and hairy or glossy leaf texture make them stand out from their other gesneriad counterparts like Aeschynanthus and Columnea. However, their seasonal or sporadic blooming period may make them undesirable to some growers.
The most commonly cultivated species of this genus are Nematanthus australis, N. gregarious, and N. wettsteinii. Their orange blossoms look like candy corn or goldfish, which is why this genus has the common name of “goldfish plant.” Other species like Nematanthus brasiliensis, N. corticola, and N. crassifolius have long pedicels that hang down from the stem. Species like Nematanthus albus are scented. Cultivars like Nematanthus gregarious ‘Golden West’ and N. gregarious ‘Dibley’s Gold’ have variegated foliage.
Although the goldfish-like orange blossoms are the most recognized blossoms on Nematanthus, the genus includes four different flower types. They are:
- A hypocyrtoid, right side up blossom like in N. australis, N. gregarious, and N. wettsteinii
- A hypocyrtoid, upside down blossom like N. fissus, N. jolyanus, and N. tessmannii.
- A hanging, upside down blossom like in N. corticola, N. crassifolius, and N. flumensis.
- A large campanulate white corolla blossom like in N. albus, N. punctatus, and N. wiehleri.
Nematanthus is closely related to Codonanthe and Codonanthopsis. They are all within the same clade of Tribe Episcieae in the New World subfamily of gesneriads Gesneriodeae. More recent DNA testing from 2013 revealed that Codonanthe is more closely related to Nematanthus than to Codonanthopsis. Nematanthus and Codonanthe grow in the same geographic area, and they share the same number of chromosomes (2n=16). In comparison, Codonanthe and Codonanthopsis differ in their geographic locations, their number of chromosomes, the shape of their fruit, and the presence of corolla spurs, extrafloral nectaries, and anther connective tissue. Hybridizers have been able to create intergeneric hybrids between Codonanthe and Nematanthus, but there are no known intergeneric hybrids with Codonanthopsis.
The genus was first created in the 1820s. The etymology of the name comes from the Greek nema meaning “thread or hair” and from anthos meaning “flower.” The name refers to the thin pedicels of the hanging blossoms on many of the species, especially in the type species Nematanthus corticola.
Nematanthus grow well in a well-drained soilless mix. They can be grown under a windowsill or under fluorescent lights with two or four lamps. Nematanthus can tolerate the typical humidity of a home of about 40%; however, their growth habit improves with increased humidity.
Because they come from the cooler temperatures at higher elevations, they are sensitive to extreme heat. At temperatures over 80°F (27°C), the plant will rapidly lose its leaves. It also loses its leaves to overwatering.
- Distribution. Nematanthus are found in the montane forests of southeastern Brazil where they grow on trees or rocks.
- Growth Habit. They can grow as subshrubs or herbs.
- Stem. The stem can grow upward, climbing, creeping, or pendent. The stem can be woody or woody only at the base, and it can have fibrous roots that grow from its nodes.
- Leaves. The leaves are opposite, and each leaf can be of different shapes or sizes. The leaves can grow directly from the stem without a petiole, or they can grow from a petiole. The leaf blade can be elliptic-shaped (oval) or obovate-shaped (ovate but with the narrow end at the base or leaf petiole). The leaves are typically hard and fleshy and they can sometimes have purple on the lower surface.
- Inflorescence. Axillary cymes with one to eight flowers. The pedicels can be short or long and usually hang down from the main stem.
- Sepals. Sepals are fused at the base of the pedicel, and they can be colored.
- Corolla. The corollas are yellow, orange, red, rose, or dark purple. The corollas of some species are upside down. The corolla tube can be cylindrical or gradually widening; can be sometimes sharply bent at the base; and can usually have a large swelling on one side making an angle of 20-90-degrees with the pedicel. The flaring outer region of the fused corolla (i.e., the limb) can have short, spreading or reflexed lobes, with a mouth that is constricted, orbicular, or pentagonal.
- Male parts. Four stamens divided in pairs of unequal length. The filaments are closely attached to the corolla base, and the anthers are connected to each other.
- Female parts. Ovary is superior, as it lies above sepals.
- Fruit. Fruit is a fleshy capsule that includes a calyx that remains on the fruit until its maturity. The fruit dehisces loculicidally, exposing the colored placentae and prominent funicle of the seeds.
- Chromosome number. 2n = 16.