page_title: Lauraceae
section_title: Classification
hierarchical_section_title: Lauraceae / Classification
caption_attribution_description: twig with leaves and unripen fruit of Ocotea obtusata, a tree species endemic to Mascarene islands (Réunion and Mauritius), sample coming from Petit Serré place (Saint-Joseph)
context_page_description: The flowering plant family Lauraceae, the laurels, includes the true laurel and its closest relatives. This family comprises about 2850 known species in about 45 genera worldwide. They are dicotyledons, and occur mainly in warm temperate and tropical regions, especially Southeast Asia and South America. Many are aromatic evergreen trees or shrubs, but some, such as Sassafras, are deciduous, or include both deciduous and evergreen trees and shrubs, especially in tropical and temperate climates. The genus Cassytha is unique in the Lauraceae in that its members are parasitic vines.
context_section_description: Classification within the Lauraceae is not fully resolved. Multiple classification schemes based on a variety of morphological and anatomical characteristics have been proposed, but none are fully accepted.  According to Judd et al. (2007), the suprageneric classification proposed by van der Werff and Richter (1996) is currently the authority. However, due to an array of molecular and embryological evidence that disagrees with the groupings, it is not fully accepted by the scientific community. Their classification is based on inflorescence structure and wood and bark anatomy. It divides Lauraceae into two subfamilies, Cassythoideae and Lauroideae. The Cassythoideae comprise a single genus, Cassytha, and are defined by their herbaceous, parasitic habit. The Lauroideae are then divided into three tribes: Laureae, Perseeae, and Cryptocaryeae.
  The subfamily Cassythoideae is not fully supported. Backing has come from matK sequences of chloroplast genes while a questionable placement of Cassytha has been concluded from analysis of intergenetic spacers of chloroplast and nuclear genomes. Embryological studies also appear contradictory. One study by Heo et al. (1998) supports the subfamily. It found that Cassytha develops an ab initio cellular-type endosperm and the rest of the family (with one exception) develops a nuclear-type endosperm.  Kimoto et al. (2006)  suggest Cassytha should be placed in the tribe Cryptocaryeae because it shares a glandular anther tapetum and an embryo sac protruding from the nucellus with other members of the Cryptocaryeae.
  The tribes Laureae and Perseeae are not well supported by any molecular or embryological studies. Sequences of the matK chloroplast gene, as well as sequences of chloroplast and nuclear genomes, reveal close relationships between the two tribes.  Embryological evidence does not support a clear division between the two tribes, either. Genera such as Caryodaphnopsis and Aspidostemon that share embryological characteristics with one tribe and wood and bark characteristics or inflorescence characteristics with another tribe blur the division of these groups.  All available evidence, except for inflorescence morphology and wood and bark anatomy, fails to support separate tribes Laureae and Perseeae.
  The tribe Cryptocaryeae is partially supported by molecular and embryological studies. Chloroplast and nuclear genomes support a tribal grouping that contains all the genera circumscribed by van der Weff and Richter (1996), as well as three additional genera. Partial support for the tribe is also attained from the matK  sequences of chloroplast genes as well as embryology.
  Challenges in Lauraceae classification
  The knowledge of the species comprising the Lauraceae is incomplete. In 1991, about 25-30% of neotropical Lauraceae species had not been described. In 2001, embryological studies had only been completed on individuals from 26 genera yielding a 38.9% level of knowledge, in terms of embryology, for this family. Additionally, the huge amount of variation within the family poses a major challenge for developing a reliable classification.
caption: Twig of Ocotea obtusata with unripe fruit with an appearance similar to an acorn
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