The Thymelaeaceae are a cosmopolitan family of flowering plants composed of 50 genera (listed below) and 898 species. It was established in 1789 by Antoine Laurent de Jussieu. The Thymelaeaceae are mostly trees and shrubs, with a few vines and herbaceous plants, the latter including some annual species.

Description

Several conspicuous or unusual traits are characteristic of the family (when Tepuianthus is excluded). The bark is usually shiny and fibrous, with strips of bark peeling down the side of broken stems. The number of stamens is usually once or twice the number of calyx lobes; when twice, they often occur in two well separated series. Exceptions include Gonystylus, which may have up to 100 stamens, and Pimelea, which has only 1 or 2.

Thymelaeaceae are often difficult to identify because of equivocal interpretation of the flower parts. Sepals, petals, and staminodes are hard to distinguish, and many keys are ambiguous about whether staminodes should be counted as stamens. Moreover, in Wikstroemia, individual plants often produce anomalous flowers.

Taxonomy

The family is named from the genus Thymelaea, the name of which is a combination of the Greek name for the herb thyme θύμος (thúmos) and that for the olive ἐλαία (elaía)—in reference to its thyme-like foliage (i.e. minuscule leaves) and olive-like fruit.

Classification

The Thymelaeaceae are in the order Malvales. Except for a sister relationship with Tepuianthaceae, little is known for sure about their relationships with the other families in the order.

Unlike most recent authors, who accept four subfamilies, B. E. Herber has divided Thymelaeaceae into two subfamilies. He has retained the subfamily Gonostyloideae, but renamed it Octolepidoideae. The other three traditional subfamilies (Synandrodaphnoideae, Aquilarioideae, and Thymelaeoideae) were combined into a Thymelaeoideae s.l.(sensu lato), and reduced to tribal rank, as Synandrodaphneae, Aquilarieae, and Daphneae, respectively. No tribes were designated in subfamily Octolepidoideae, but it was provisionally divided into two informal groups, the Octolepis group and the Gonystylus group. Likewise, no subtribes were designated in the tribe Daphneae, but it was informally divided into four groups: the Linostoma group, the Daphne group, the Phaleria group, and the Gnidia group. The 45 genera accepted by Herber are grouped as follows. Three genera in Daphneae were placed incertae sedis (not assigned to any particular group or in a separate group by themselves).

Octolepidoideae

:Octolepis group: Arnhemia, Deltaria, Lethedon, Octolepis, Solmsia

:Gonystylus group: Aetoxylon, Amyxa, Gonystylus

Thymelaeoideae

:Synandrodaphneae: Synandrodaphne

:Aquilarieae: Aquilaria, Gyrinops

:Daphneae

::Linostoma group: Craterosiphon, Dicranolepis, Enkleia, Jedda, Linostoma, Lophostoma, Synaptolepis

::Phaleria group: Peddiea, Phaleria

::Daphne group: Daphne, Daphnopsis, Diarthron, Dirca, Edgeworthia, Funifera, Goodallia, Lagetta, Ovidia, Rhamnoneuron, Schoenobiblus, Stellera, Thymelaea, Wikstroemia

::Gnidia group: Dais, Drapetes, Gnidia, Kelleria, Lachnaea, Passerina, Pimelea, Struthiola

::Incertae sedis: Linodendron, Stephanodaphne, Lasiadenia

Phylogeny

The first molecular phylogeny for Thymelaeaceae was published in 2002. but there was not sufficient sampling in Wikstroemia and Daphne to exclude the possibility that Thymelaea, Diarthron, and others might be embedded in them.

The large genus Gnidia is polyphyletic and its species fall into four separate clades, each of which contains other genera of the family (see the phylogenetic tree below). The type species for Gnidia is Gnidia pinifolia. If Gnidia is divided into four or more separate genera, the segregate genus which contains G. pinifolia will retain the name Gnidia. Zachary S. Rogers published a revision of the Gnidia of Madagascar in 2009 in Annals of the Missouri Botanical Garden.

Some of the older treatments of Thymelaeaceae treat Lasiosiphon as a separate genus from Gnidia. This distinction was later shown to be artificial. However, Van der Bank et al. (2002) suggested that Lasiosiphon might be resurrected if redefined. The type species for Lasiosiphon is Gnidia glauca, formerly known as Lasiosiphon glaucus.

Open questions

Rautenbach used different names from Herber for some of the groups and placed some of the groups at different taxonomic rank, but her phylogeny supports Herber's classification with the few exceptions noted below. The only strongly supported difference (99% (bootstrap percentage) from Herber's classification was that Dais was found to be sister to Phaleria. The phylogeny casts significant doubt upon the monophyly of the subfamily Octolepidoideae, and upon the monophyly of the informal Octolepis and Gonostylus groups, but this result had only weak statistical support. Only a sampling of more species and more DNA from each will determine whether these groups are monophyletic or not. Stephanodaphne and Peddiea might need to be transferred to the Gnidia group, but support was not strong (60% BP) for a clade consisting of the Gnidia group with Stephanodaphne and Peddiea. Again, more extensive sampling will be required to resolve this question. Two of the three genera placed incertae sedis by Herber (Linodendron and Lasiadenia) have not yet been sampled and their relationships to other genera remain obscure.

Genera

thumb|upright|right|[[Gonystylus bancanus native to Brunei, Indonesia, and Malaysia: botanical line drawing of detailed anatomy]]

Herber (2003) accepts 45 genera, excluding Tepuianthus from the family, sinking Atemnosiphon and Englerodaphne into Gnidia, Eriosolena into Daphne, and Thecanthes into Pimelea.

{| border="0"

|-

| style="vertical-align:top;"|

  • Aetoxylon
  • Amyxa
  • Aquilaria
  • Arnhemia
  • Atemnosiphon
  • Craterosiphon
  • Dais
  • Daphne
  • Daphnimorpha
  • Daphnopsis
  • Deltaria
  • Diarthron
  • Dicranolepis
  • Dirca
  • Drapetes
  • Edgeworthia
  • Englerodaphne

| style="vertical-align:top;"|

  • Enkleia
  • Eriosolena
  • Funifera
  • Gnidia
  • Gonystylus
  • Goodallia
  • Gyrinops
  • Jedda
  • Kelleria
  • Lachnaea
  • Lagetta
  • Lasiadenia
  • Lethedon
  • Linodendron
  • Linostoma
  • Lophostoma
  • Octolepis

| style="vertical-align:top;"|

  • Ovidia
  • Passerina
  • Peddiea
  • Phaleria
  • Pimelea
  • Restella
  • Rhamnoneuron
  • Schoenobiblus
  • Solmsia
  • Stellera
  • Stephanodaphne
  • Struthiola
  • Synandrodaphne
  • Synaptolepis
  • Tepuianthus
  • Thymelaea
  • Wikstroemia

|}

In the past, different authors have defined Thymelaeaceae in different ways. For example, John Hutchinson excluded Gonystylus and its close relatives, as well as Aquilaria and its close relatives from the family, forming two segregate families, Gonystylaceae and Aquilariaceae. But today, the only controversy that still remains over the circumscription of the family is the question of whether Tepuianthus should be included, or segregated as a separate, monogeneric family. Stevens includes Tepuianthus, but Kubitzki treats Tepuianthaceae as a separate family.

Distribution

The family is more diverse in the Southern Hemisphere than in the Northern, with major concentrations of species in Africa and Australia. The genera are overwhelmingly African.

Ethnobotany and economic use

thumb|upright|Lagetta lagetto the "lacebark": botanical illustration showing plant with samples of cordage and fabric made from its fibre

thumb|upright|right|Intricate [[Jamaican souvenirs woven from "lacebark" fibre]]

thumb|upright|right|The [[Brazilian Funifera utilis, its genus named from the suitability of its fibre for rope-making (under the obsolete name Lagetta funifera)]]

Several genera are of economic importance. Gonystylus (ramin) is valued for its comparatively soft, easily worked yellowish wood, but trade in all species in the genus is controlled by CITES. Many genera have inner bark yielding strong fibre suitable for the making of cordage and paper, a fact acknowledged in the naming of one of the genera, Funifera meaning the Latin for "bearer (provider) of rope". The bark of Aquilaria, Daphne, Edgeworthia, Gnidia, Linostoma, Rhamnoneuron, Thymelaea, Stellera, and Wikstroemia are used in paper-making, while Lagetta was once harvested as a source of natural lace for making doilies and trimmings for luxury garments.

Toxicity and medicinal uses

thumb|The attractive, but poisonous, fruit of [[Daphne mezereum]]

Many of the species (e.g. Wikstroemia indica and Stellera chamaejasme) have actual or potential uses in medicine and are poisonous if eaten, acting as violent purges (e.g. Daphne mezereum). This toxicity is often related to the plants' containing phorbol esters which, as the name suggests, are also common in the spurge family Euphorbiaceae.

Use as ornamental plants

thumb|upright|right|The sweetly-scented and highly ornamental flowers of [[Daphne bholua, a Nepalese species also used in traditional paper-making]]

Daphne is grown (despite the high toxicity of its attractive fruit) for its sweetly scented flowers. Species of Wikstroemia, Daphne, Phaleria, Dais, Pimelea and other genera are grown as ornamental plants.

<gallery>

File:Strettle Road Reserve pimelea.jpg|Inflorescence of the Australian Pimelea spectabilis

File:Daphne striata 100604.jpg|Daphne striata, native to the Alps and the Dolomites

File:Struthiola ciliata Gonnabos IMG 1983s.jpg|The South African Struthiola myrsinites

File:Passerina (Thymelaeaceae) details of flowering sprig EOS 009.jpg|Flowers of an unidentified Passerina species

File:Hortus Botanicus Leiden - Phaleria capitata Jack (Sumatra).JPG|Phaleria capitata of Sumatra exhibiting cauliflory

File:Stellera chamaejasme 2.jpg|Stellera chamaejasme of Central and East Asia

File:Daphnopsis racemosa Envira flor Oct 2007 031.jpg|Flower of Daphnopsis racemosa

File:Daphnopsis racemosa Griseb. (17144500699).jpg|Fruit of Daphnopsis racemosa

File:Dirca palustris - Edwards.jpg|Flowers of Dirca palustris from the United States

File:Akabana-mitsumata.JPG|Edgeworthia chrysantha, native to China

File:Wikstroemia phillyreifolia (Hawai'i false ohelo) flowers (6592426883).jpg|Flowers of the Hawaiian Wikstroemia phillyreifolia

</gallery>

References

  • Zachary S. Rogers (2009 onwards). A Worldwide Checklist of Thymelaeaceae (version 1).
  • Angiosperm Phylogeny Peter F. Stevens (2001 onwards) In: Missouri Botanical Garden
  • Rautenbach (2008) in: UJDigiSpace @ The University of Johannesburg
  • Distribution in: Gnidia is not monophyletic: taxonomic implications for Gnidia and its relatives in Thymelaeoideae
  • Thymelaeaceae of Mongolia in FloraGREIF