Thymelaeaceae

Thymeleaeaceae
Daphne striata
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Rosids
Order: Malvales
Family: Thymelaeaceae
Genera

See text

The Thymelaeaceae /ˌθɪmᵻliːˈeɪsiː/ are a cosmopolitan family of flowering plants composed of 50 genera (listed below) and 898 species.[1] It was established in 1789 by Antoine Laurent de Jussieu.[2]

The Thymelaeaceae are in the order Malvales.[3] Except for a sister relationship with Tepuianthaceae, little is known for sure about their relationships with the other families in the order.[4]

The family is more diverse in the southern hemisphere than in the northern, with a major concentrations of species in Africa and Australia.[5] The genera are overwhelmingly African [6]

The Thymelaeaceae are mostly trees and shrubs, with a few vines and herbaceous plants.

Several genera are of economic importance. Gonystylus (Ramin) is valued for its hard, white wood. The bark of Edgeworthia and Wikstroemia is used as a component of paper, while Lagetta species are known as lacebark for their lacelike inner bark, which has been used to make clothing and utilitarian objects.

Daphne is grown for its sweetly scented flowers. Species of Wikstroemia, Daphne, Phaleria, Dais, Pimelea and other genera are grown as ornamentals.[7][8]

Many of the species are poisonous if eaten.

A good collection of pictures of plants in this family has appeared in a scientific paper.[8]

Herber (2003)[9] recognized 45 genera, excluding Tepuianthus from the family, sinking Atemnosiphon and Englerodaphne into Gnidia, Eriosolena into Daphne, and Thecanthes into Pimelea.[9]

The largest genera and the approximate number of species in each are Gnidia (160), Pimelea (110), Daphne (95), Wikstroemia (70), Daphnopsis (65), Struthiola (35), Lachnaea (30), Thymelaea (30), Phaleria (30), and Gonystylus (25).[9]

Genera

As of December 2014, 50 genera are accepted by the World Checklist of Thymelaceae:[10]

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 2 segregate families: Gonystylaceae and Aquilariaceae.[11] 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.[12] Stevens includes Tepuianthus, but Kubitzki treats Tepuianthaceae as a separate family.[13]

Description

This is not intended as a full botanical description, but only as a few notes on some of the conspicuous or unusual traits of the family when Tepuianthus is excluded. The bark is usually shiny and fibrous. Attempts to break the stem often result in a strip of bark peeling down the side. The number of stamens is usually once or twice the number of calyx lobes. If twice, then they often occur in 2 well separated series. Exceptions include Gonystylus, which may have up to 100 stamens, and Pimelea, which has only 1 or 2. The floral tube appears to be a calyx or corolla, but is actually a hollow receptacle.[8] This feature is probably unique to Thymelaeaceae. The sepals are mounted on the rim of the floral tube. Stamens may be mounted on the rim or inside. What appear to be petals are actually stipular appendages of the sepals. The fruit is a 1-seeded berry or an achene. The 1-seeded berries have often been mistaken for drupes whenever the seed coat was mistaken for an endocarp.

When using a key to the families of flowering plants, Thymelaeaceae are often difficult or impossible to recognize 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.[14] In these, the nonfunctional organs are much deformed and bear little resemblance to the parts that they represent.

Defining the genera

The circumscription of genera in Thymelaeaceae has always been especially difficult, and is to some degree, artificial. For example, the difficulty of distinguishing Daphne from Wikstroemia has been commented upon by Rautenbach and Herber.[8][9] Several small genera are probably embedded in Daphne or Wikstroemia, or if Daphne and Wikstroemia are intermingled, these small genera might be embedded in both simultaneously. Stellera, for example, is nested within Wikstroemia, at least (see the phylogenetic tree below).

A recent comparison of DNA sequences has established the monophyly of Thymelaea and the polyphyly of Diarthron,[15] 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 4 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 4 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 recognize Lasiosiphon as a separate genus from Gnidia. This distinction was later shown to be artificial. However, Van der Bank et al. (2002)[16] suggested that Lasiosiphon might be resurrected if redefined. The type species for Lasiosiphon is Gnidia glauca, formerly known as Lasiosiphon glaucus.

Classification

Unlike most recent authors, who recognize 4 subfamilies, B.E. Herber has divided Thymelaeaceae into 2 subfamilies. He has retained the subfamily Gonostyloideae, but renamed it Octolepidoideae. The other 3 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 2 informal groups, the Octolepis group and the Gonystylus group. Likewise, no subtribes were designated in the tribe Daphneae, but it was informally divided into 4 groups: the Linostoma group, the Daphne group, the Phaleria group, and the Gnidia group. The 45 genera recognized 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).

Octolepidoidae

Octolepis group: Arnhemia, Deltairia, 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: Phaleria, Peddiea
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.[16] It was based on 2 regions of chloroplast DNA. These were the rbcL gene and the intergenic spacer between the transfer RNA genes trnL and trnF. Forty one species in the family were sampled. In 2008, Marline Rautenbach performed a phylogenetic study in which 143 species in the family were sampled. The sampling in this study was concentrated in the Gnidia group, but the sampling in the rest of the family was as extensive as in the previous study, or more so. In addition to rbcL and trnL-F data, sequences of the ITS (internal transcribed spacer) region of nrDNA (nuclear ribosomal DNA) were used. All of the clades that were strongly supported in the previous study were recovered with even stronger statistical support.

The tree below is an excerpt from the Rautenbach (2002) phylogeny. The species of Gnidia were chosen from among the most common or well known species in a way that shows which clades contain species of Gnidia.

Octolepis

Gonystylus

Lethedon

Deltairia

Solmsia

Arnhemia



Thymelaeoideae 
Synandrodaphneae 

Synandrodaphne
Aquilarieae 

Aquilaria

Gyrinops



Daphneae 
Linostoma group 

Dicranolepis

Enkleia

Synaptolepis

Craterosiphon
Daphne group 

Edgeworthia


Wikstroemia gemmata

Wikstroemia canescens

Stellera

Diarthron

Daphne

Thymelaea
Phaleria group 

Phaleria

Dais



Gnidia group 


Gnidia glauca

Gnidia kraussiana

Gnidia calocephala

Stephanodaphne

Dirca

Ovidia

Peddiea

Gnidia humilis

Gnidia squarrosa

Gnidia pilosa

Pimelea


Gnidia racemosa

Gnidia pinifolia

Struthiola

Lachnaea

Passerina

Drapetes

Gnidia anomala











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 3 genera placed incertae sedis by Herber (Linodendron and Lasiadenia) have not yet been sampled and their relationships to other genera remain obscure.

References

  1. ↑ Zachary S. Rogers (2009 onwards). A World Checklist of Thymelaeaceae (version 1). Missouri Botanical Garden Website, St. Louis.
  2. ↑ Antoine Laurent de Jussieu Genera Plantarum, page 76. Herrisant & Barrois, Paris.
  3. ↑ Peter F. Stevens (2001 onwards) Angiosperm Phylogeny Website In: Missouri Botanical Garden Website
  4. ↑ Clemens Bayer, Michael F. Fay, Anette Y. de Bruijn, Vincent Savolainen, Cynthia M. Morton, Klaus Kubitzki, William S. Alverson, and Mark W. Chase (1999). "Support for an expanded family concept of Malvaceae within a recircumscribed order Malvales: a combined analysis of plastid atpB and rbcL DNA sequences". Botanical Journal of the Linnean Society 129(4): 267-381
  5. ↑ Vernon H. Heywood, Richard K. Brummitt, Alastair Culham, and Ole Seberg. Flowering Plant Families of the World. Firefly Books: Ontario, Canada (2007)
  6. ↑ Marline Rautenbach. Figure 1.2, page 7 In: "Gnidia is not monophyletic: taxonomic implications for Gnidia and its relatives in Thymelaeoideae" Digispace at the University of Johannesburg. 8 Jul 2008. (see External links below).
  7. ↑ George W. Staples and Derral R. Herbst. 2005. "A Tropical Garden Flora". Bishop Museum Press: Honolulu. ISBN 978-1-58178-039-0.
  8. 1 2 3 4 Marline Rautenbach. "Gnidia is not monophyletic: taxonomic implications for Gnidia and its relatives in Thymelaeoideae". Digispace at the University of Johannesburg 8 Jul 2008. (see External links below)
  9. 1 2 3 4 B.E. Herber. "Thymelaeaceae" In: The Families and Genera of Vascular Plants vol.V (Klaus Kubitzki and Clemens Bayer, volume editors). Springer-Verlag: Berlin, Heidelberg (2003)
  10. ↑ Rogers, Z.S. (2009). "A World Checklist of Thymelaeaceae (version 1)". Missouri Botanical Garden, St. Louis.
  11. ↑ Hutchinson,John. The Families of Flowering Plants, Third Edition (1973). Oxford University Press: London.
  12. ↑ Horn,J.W., (2004). "The morphology and relationships of the Sphaerosepalaceae(Malvales)". Botanical Journal of the Linnean Society 144(1):1-40
  13. ↑ Klaus Kubitzki. "Tepuianthaceae" In: The Families and Genera of Vascular Plants, vol.V Klaus Kubitzki and Clemens Bayer. (volume editors). Springer-Verlag: Berlin,Heidelberg. (2003).
  14. ↑ Warren L. Wagner, Derral R. Herbst, and Sy H. Sohmer. Manual of the Flowering Plants of Hawaii, Revised Edition, 1999. Bishop Museum Press: Hololulu
  15. ↑ David Galicia-Herbada (2006). "Origin and diversification of Thymelaea(Thymelaeaceae): inferences from a phylogenetic study based on ITS (rDNA) sequences". Plant Systematics and Evolution 257(3-4):159-187.
  16. 1 2 Michelle van der Bank, Michael F. Fay, and Mark W. Chase (2002). "Molecular Phylogenetics of Thymelaeaceae with particular reference to African and Australian genera". Taxon 51(2):329-339.
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