By: Petra

My first encounter with any gesneriad was, of course, saintpaulia hybrid collection my granny kept at home. But I really fell in love with them when a rescued Aeschynanthus speciosus flowered for the first time. I didn't have a clue what kind of plant it was and in the pre-internet era spent some time browsing through stacks of books trying to figure out what it was. And that first flower is still a treasured memento among the pages of Heywoods Flowering Plants.

I hope that through this article you too will come to appreciate gesneriads a bit more.

Gesneriads are a large family of dicot herbs and shrubs. Many species are epiphytic. Most species are tropical and are mainly distributed in the Southern hemisphere. Gesneriads are interesting to gardeners as many species make nice ornamental plants, geologists' count them among evidence of continental drift, and botanists are fascinated by them all the time. The family name is based on the genus Gesneria , which honors Swiss humanist Conrad Gessner. Gesneriads are not present in the flora of Slovenia, however two species of Ramonda are found in the area of former Yugoslavia: one in Serbia and one in Macedonia.

A couple of questions are provoked at viewing the gesneriad distribution map : how and why had one group of plants come to inhabit only the southern continents? The other, for European plant fans intriguing question is how did those few species manage to get to the mountains of Southern Europe?

Before we try to answer, let's take a look at two scientific facts:

The first – paleobotanical: The ancestors of flowering plants diverged from gymnosperms around 245–202 million years ago, and the first flowering plants known to exist are from 140 million years ago. They diversified enormously during the Lower Cretaceous and became widespread around 100 million years ago, but replaced conifers as the dominant trees only around 60–100 million years ago.

The second – paleogeographic: The ancient supercontinent Pangaea broke apart to form Laurasia and Gondwana. Gondwana was comprised by embryonic present day South America, Africa, Arabia, Antarctica, Australia, Indian subcontinent and a few other smaller parts. Gondwana began to break up in the Lower Jurassic around 184 million years ago, accompanied by massive eruptions of basalt lava, as East Gondwana, comprising Antarctica, Madagascar, India and Australia, began to separate from West gondwana (Africa and South America). The Red Sea and East African Rift are modern examples of the continuing dismemberment of Gondwana. By the way, the East African Rift is the cradle of human kind.

Diagnostic features

Gesneriads are rare in Africa, but in America are often regarded as tropical counterparts of the essentially temperate family Scrophulariaceae . This view needs specification and partly correction. In contrast to traditional belief Gesneriaceae are not an offspring of Scrophulariaceae , but seem to have an independent origin. Though most genera and species occur in the tropics, in phylogeny the tropical areas seem to have been secondarily invaded from warm-temperate and subtropical regions. Therefore the distribution of gesneriads is not at all parallel with primarily tropical plants such as palms ( Arecaceae ) as their origin is most probably extra-tropical.

Gesneriads are herbs and shrubs, rarely trees. They have opposite or alternate, sometimes basal leaves (rarely a single leaf), which are simple, entire or toothed (rarely pinnatisect), and without stipules. The underground parts may be fibrous, woody tubers, scaly rhizomes or aerial stolons. The flowers are bisexual, irregular and borne in racemes, cymes or singly. There are five sepals, free or tubular at the base, with five petals also fused into a basal tube, the free ends being oblique, two-lipped or rarely rotate. The two or four stamens often cohere in pairs and release pollen by longitudinal slits. The ovary is superior or inferior and has a single locule containing numerous ovules, usually on two parietal or intrusive placentas. The style is single, crowned with a two-lobed or mouth-shaped stigma. An annular, lobed or one-sided nectary lies between the ovary and petals. The fruits are rounded or elongated capsules or rarely berries, and contain many small seeds, with or without endosperm, and with straight embryos.

Distribution and systematics within the family

There are at least 125 genera and somewhere between 2000 and 3200. There are a few synonyms, some genuses may be too narrowly or too widely defined and each year botanists discover a new species or two.

Most gesneriads are distributed pantropically and pansubtropically (Old and New World tropics and subtropics): both Americas from Mexico southwards, East, West and South Africa, Madagascar, Southeast Asia, Polynesia and Australasia. There are a few transgressions into temperate climates: to the north (Europe: Pyrenees, Balkan Peninsula; Asia: Himalayas, China including Northern China) and the south (SE Australia, New Zealand, S Chile). In Asia-Malesia and in America are around 60 genera endemic to each. In Africa there are 9 genera (around 160 species) in Europe 3 genera (6 species). Nine genera (20 species) have a distinctly southern hemisphere distribution. Two genera have transcontinental distributions: Rhynchoglossum is represented both in Asia and in the neotropics (with only R. azureum ), Epithema ( E. tenue in W Africa) and around 20 other in Mainland Asia and Malesia.

Gesneriaceae can be divided into two subfamilies: Cyrtandroideae and Gesnerioideae . About half the genera are placed in each of the two subfamilies. The subfamilies differ in that in Cyrtandroideae the cotyledons are of unequal length and in Gesnerioideae they are equal. This division is supported by data from pigment chemistry and chromosome number patterns. Each of the subfamilies are then divided into tribes. However let's split each subfamily into two larger groups, respectively, for an easier explanation of distribution. Let's divide Cyrtandroideae into epithematoid and didymocarpoid gesneriads and Gesnerioideae into gesneroid and coronantheroid gesneriads.

Epithematoid : South and Southeast Asia to New Guinea, one species of Epithema ( E. tenue ) in West Africa and one species of Rhynchoglossum ( R . azureum ) in Central America to Venezuela.

Didymocarpoid : South, East and Southeast Asia, the Philippines, the Malay archipelago from Sumatra to New Guinea (the bulk of genera roughly inhabits the area of Indonesia), Polynesia (Cyrtandra). East, West and South Africa, Madagascar (Streptocarpus and allies); southern Europe (Ramonda, Haberlea, Jancaea ).

Coronantheroid : Restricted to the southern hemisphere; NE Australia (Lenbrassia) , SE Australia ( Fieldia ), SW Pacific islands (Negria on Lord Howe Island), Solomon Islands (one sp. of Coronanthera), New Caledonia (Coronanthera , Depanthus), New Zealand ( Rhabdothamnus ), and temperate South America (Chile and adjacent Argentina: Mitraria, Sarmienta, Asteranthera ).

Gesnerioid : Southern North America (central and southern Mexico), Central America and tropical South America, southwards to SE Brazil and Northern Argentina and Uruguay (esp. Sinningia and allies).

A journey around the world

Gesneriads probably evolved in the area of present-day South America 70 million years ago. Subfamily Cyrtandroideae soon dispersed to what is now Africa, where many new forms evolved. When this pre-Africa began to crumble some pieces of then Northern Africa crept north and became Southern Europe – this is how the ancestors of Jankaea, Ramonda and Haberlea arrived to the areas that will become Pyrenees mountains and Balkan peninsula ... they piggybacked! Cyrtandroids managed to colonize Madagascar and India at the time when they were either already islands or still joined to East Gondwana, respectively. In any case cyrtandroids were carried on India North, where they witnessed the rise of the Himalayas when the Indian plate drove into the southern edge of the Eurasian plate. From there cyrtandroids had an open road to the Eastern and SE Asia and across the Pacific islands all the way to Hawaii. With the help of molecular analyses the evolution of Cyrtandra , the largest gesneriad genus, with 600 species, and the sequence by which it colonized new habitats (islands) this can be tracked, for example, over Indonesian islands to Polynesia. Cyrtandroids arrived to Japan in a similar manor as they did to Southern Europe.

There are no gesneriads belonging to Gesnerioideae in Africa, so they likely took a different – Southern – route to the East; along the Southern South America to Antarctica, which had a temperate climate back then, but is now only inhabited by 4 native angiosperm species. From Antarctica gesnerioids spread east to Australia, which was still joined to Antarctica. And finally from Australia East again to New Zealand, New Caledonia and other Southwestern Pacific islands.

Co-evolving with birds

Evolution of about half of the New World gesneriads have been partly by co-adaptation with bird pollinators, notably the hummingbird family which is restricted to the Americas. Typical hummingbird flowers are two-lipped, often red as in Columnea, Asteranthera and some Sinningia species (this is because birds are attracted to red / reddish colors). Other pollinators such as bees, bats, butterflies, moths and flies have also been active in gesneriad evolution. In Hypocyrta, Besleria and Alloplectus some species have pouched corollas with constricted throats, the significance of which is still not clear. The Old World genus Aeschynanthus is considered a parallel development with Columnea in being bird-pollinated. Flowers are an important part of the pollination system in gesneriads but extra-floral attraction also exists in some species, such as strikingly colored leaf- and sepal-hairs, or leaf pigmentation with stained-glass-like optical properties when viewed against the light.

Distant relatives

Herbaceous families related to the Gesneriaceae are the Scrophulariaceae, Orobanchaceae , and Lentibulariaceae ; the chiefly woody Bignoniaceae is also florally similar but has woody fruits that often have two locules, and winged seeds, as well as divided leaves. The gesneriad ovary may be superior, as in Scrophulariaceae , or inferior, but in contrast to the Scrophulariaceae the ovary usually has a single locule not two. The usually parietal placentas of gesneriads with superior ovaries differ from the basal placentas of butterworts ( Lentibulariaceae ). Orobanches are parasites and lack chlorophyll, so also differ from gesneriads. Several molecular systematic studies have shown that Gesneriaceae are actually not closely related to any other family of the Lamiales . However more recently a sister-group relationship with Calceolariaceae has been suggested. Calceolariaceae have recently been elevated to family status, but had been until then included in Scrophulariaceae . Other studies have suggested that two genera generally placed in other families, Sanango and Peltanthera , are more closely related to Gesneriaceae than to any other members of the Lamiales but there is as yet no consensus on whether those genera should be included in the family.

The Serbian phoenix flower

There are 3 species in the genus Ramonda ; all are peleoendemites (relictual endemites) in the mountains of Southern Europe. Ramonda myconi grows in Central and South Pyrenees mountains of Spain and France. Ramonda nathaliae is found only in the mountains of Northern Albania, Northern Greece and Macedonia. The third species is Ramonda serbica , a tertiary relict endemic to Jelasnica and Sicevacka Gorge in Serbia. And this small plant has an amazing story; this plant is also known as the Serbian phoenix flower since it can survive completely drying out. This is undoubtedly an essential adaptation as it grows naturally in crevices on bare rock, substrate that can quickly and completely dry out. The story of how this adaptation was discovered goes like this: in 1928 a Russian botanist Pavel Chernavsky made a herbarium that included this plant. Accidentally he spilled a glass of water over a herbarium sheet with a dead and dried Ramonda serbica . Several days later, to his astonishment he saw that the 'dead' plant not only regenerated but also came into flower. The same year he published this chance but major discovery in the Russian Botanic Journal. This type of plant is scientifically referred to as a resurrection plant and yes, there are a few others known – but let's leave them for another story.

Gesneriads and people

Some species have been reported as being used in rural medicine, but the importance of the family lies in its cultivated ornamentals. Popular garden and house-plant genera include Achimenes , Columnea, Episcia, Gesneria, Haberlea, Hypocyrta, Kohleria, Mitraria, Ramonda, Saintpaulia (African violet), Sinningia (Gloxinias), Smithiantha, Streptocarpus (Cape primrose) and Aeschynanthus .

If you wish to propagate your favorite gesneriad house plant, there are three easy methods depending on the type of plant you have – just pop the correct part of the plant in a cup of water and wait for a few weeks until it strikes roots:

1. Rosette-forming plants like Saintpaulia and Streptocarpus are propagated by leaf cuttings

2. Plants with long stems like Aeschynanthus and Columnea are propagated by stem tip cuttings approx. 10 cm long.

3. Plants that form stolons like Episcia and Kohleria are propagated by division (replanting) of established plantlets.

Introduction to gesneriad diversity

Notable New World genera include:

Columnea, l50 species of shrubs and climbers, often epiphytic;

Sinningia, 60 species of herbs, some popularly known as gloxinias;

Achimenes, 20 species of often hairy herbs with red to blue flowers;

Episcia, 40 species of small trailing evergreens;

Gesneria (47 species) and Rhytidophyllum (20 species), two related genera with yellow-green, white or red flowers;

Gloxinia (not to be confused with the popular gloxinias), 15 species of herbs with lilac bell-flowers or cinnabar-red pouched flowers;

Smithiantha, 4 Mexican species with green or purple-brown velvety leaves and pyramids of orange-red or yellowish tubular flowers;

Phinaea, 10 species with whitish flowers;

Kohleria, 20 species often with racemes of orange-red flowers patterned inside with contrasting spots and with brown-green velvety hairy leaves.

Notable Old World genera include:

Ramonda, 3 species of stemless hairy herbs from southern Europe with showy flowers on leafless scapes;

Jankaea (1 species) and Haberlea (1 species), rosette alpines with lilac or violet flowers native to southern Europe;

Conandron, 3 Japanese species of alpine rosette herbs regarded as the counterpart of Ramonda;

Titanotrichum, with a single species from China and Taiwan, with tubular flowers bright yellow outside, blotched red-brown with a narrow yellow margin inside;

Chirita, 80 species of tropical Asian herbs with fleshy, often transparent parts and large whitish, blue, purplish or yellow clustered flowers;

Cyrtandra, 600 species from Southeast Asia and Oceania;

Aeschynanthus, 70 species of trailing or climbing shrubs from the Far East;

Petrocosmea, 15 species from Southeast Asia similar to Saintpaulia ;

Saintpaulia, 12 East African species mostly of rosette herbs;

Streptocarpus, 130 African species of evergreen herbs often with foxglove-like flowers;

Index of gesneriad genuses:

Acanthonema

Achimenes

Aeschynanthus

Agalmyla

Allocheilos

Alloplectus

Allostigma

Alsobia

Amalophyllon

Ancylostemon

Anetanthus

Anna

Asteranthera

Beccarinda

Bellonia

Besleria

Boea

Boeica

Bournea

Briggsia

Briggsiopsis

[Brookea]

Calcareoboea

Cathayanthe

Championia

[Charadrophila]

Chautemsia

Chirita

Chiritopsis

Chrysothemis

Cobananthus

Codonanthe

Codonanthopsis

Colpogyne

Columnea s.l. ( incl. Dalbergaria, Pentadenia,Trichantha, Bucinellina)

Columnea s.str.

Conandron

Corallodiscus

Coronanthera

Corytoplectus

Crantzia

Cremersia

Cremosperma

Cremospermopsis

[Cubitanthus]

Cyrtandra

[Cyrtandromoea]

Dayaoshania

Deinocheilos

Deinostigma

Depanthus

Diastema

Didissandra

Didymocarpus

Didymostigma

Dolicholoma

Drymonia

Emarhendia

Episcia

Epithema

Eucodonia

Fieldia

Gasteranthus

Gesneria

Glossoloma

Gloxinella

Gloxinia

Gloxiniopsis

Goyazia

Gyrocheilos

Gyrogyne

Haberlea

Hemiboea

Hemiboeopsis

Henckelia

Heppiella

Hexatheca

Hovanella

Isometrum

Jancaea

Jerdonia

Kaisupeea

Kohleria

Lagarosolen

Lampadaria

Lembocarpus

Lenbrassia

Leptoboea

Linnaeopsis

Litostigma

Loxonia

Loxostigma

Lysionotus

Mandirola

Metabriggsia

Metapetrocosmea

Micraeschynanthus

Mitraria

Monophyllaea

Monopyle

Moussonia

Napeanthus

Nautilocalyx

Negria

Nematanthus

Neomortonia

Niphaea

Nodonema

Nomopyle

Oerstedina

Opithandra

Orchadocarpa

Oreocharis

Ornithoboea

Paliavana

Paraboea

Paradrymonia

Paraisometrum

Paralagarosolen

Pearcea

Petrocodon

Petrocosmea

Pheidonocarpa

Phinaea

Phylloboea

Platystemma

Primulina

Pseudochirita

Ramonda

Raphiocarpus

Reldia

Resia

Rhabdothamnopsis

Rhabdothamnus

Rhoogeton

Rhynchoglossum

Rhynchotechum

Rhytidophyllum

Ridleyandra

Rufodorsia

Saintpaulia

[Sanango]

Sarmienta

Schizoboea

Seemannia

Senyumia

Sepikea

Shuaria

Sinningia

Smithiantha

Solenophora

Sphaerorrhiza

Spelaeanthus

Stauranthera

Streptocarpus

Tengia

Tetraphyllum

Thamnocharis

Titanotrichum

Trachystigma

Tremacron

Trisepalum

Tylopsacas

Vanhouttea

Wentsaiboea

Whytockia

Literature:

Heywood V. Flowering plants of the world. Abingdon. Andromeda Oxford Limited 1993.

www.wikipedia.com

www.gesneriadresearchcenter.blogspot.com

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