Centre for Plant Biodiversity Research
CPBR Summer Scholarship
Supervisor: Rogier de Kok
Teucrium is a genus of small shrubs and woody based herbs. Teucrium species are easily recognised by their distinctive flower morphology. The upper lip of the Teucrium corolla is greatly reduced, while the bottom is large and five lobed. The stamens and stigma are greatly exerted and arranged to brush the pollinator's back. There are around three hundred species world wide, with the greatest diversity found around the Mediterranean. They are, however, found world wide. There are approximately thirteen endemic Australian species of Teucrium distributed through out all states.
The division of the genus into sections has largely followed Bentham's 1835 system. This is based on calyx morphology and inflorescence type. Kastner (1989) produced the first substantial revision of the sectional divisions by including corolla and vegetative characters. Kastner, using written descriptions, tentatively included six Australian species in this revision.
This study aimed to clarify the infra generic relationships of Australian Teucrium species, and also to establish position of Australian Teucrium within the genus world wide. This was accomplished by the analysis of macro and mircomorphological characters supplemented by molecular evidence. In addition, the monotypic genera Oncinocalyx, in Eastern Australia and Teucridium, found in New Zealand, were examined. These genera were previously placed in the Verbenaceae, but their similarity to Teucrium has resulted in their being moved into the Lamiaceae. It was hoped that a clearer understanding of their status might be attained.
Sources of material
Plant material for morphological and micromorphological study was sourced from herbarium specimens housed at the Australian National Herbarium, Canberra, and the Royal Botanic Gardens, Sydney. Material for DNA extraction was from the Australian National Botanic Gardens, Canberra and from horticultural sources. Other DNA sequences were obtained from other authors via Genbank.
Numerical and cladistic analyses were conducted, requiring two morphological data sets. Characters coded included leaf length, internode length and ratio of the fused portion of the calyx to the lobed portion. The surface ornamentation of the nutlets was also examined using a scanning electron microscope.
The chloroplast gene rbcL was chosen, primarily because Teucrium sequences by other authors were available. DNA was extracted from fresh and frozen material using the CTAB method. The rbcL gene was then amplified by polymerase chain reaction and sequenced.
Both numerical analyses and the molecular data suggested that the Australian Teucrium species fall into two distinct groups. The first, for convenience named the 'T. racemosum group,' contains the bulk of Australian Teucrium species. The T. racemosum group includes T. racemosum, T. corymbosum, T. integrifolium and the West Australian species including T. eremaeum and T. myriocladum. In addition, the analyses suggested that it is affiliated with T. fruticans and T. parvifolium. Both these species are Mediterranean representatives of section Teucrium, and it would appear the this group of Australian Teucrium species belongs to this section.
The numerical analysis highlighted several affiliations within the T. racemosum group. T. eremaeum and T. myriocladum possess morphological features that set them apart from the East Australian and Australia wide species. The most striking include minute, appressed leaves with very short internodes. This group of species appears to be confined to the south west of the state, and long isolation from the east Australian species could account for its distinctiveness. The other endemic Western Australian species, T. pilbaranum, has broader tripartite leaves and longer internodes, suggesting that it is affiliated with T. albicaule and the east Australian species. T. corymbosum and T. species D. are also closely related, and differ in the indumentum type and leaf proportions.
The second group, the T. argutum group includes T. ajugaceum, T. sp A. and T. sp C. The distinctiveness of this group amongst Australian species was evident in all analyses. Unfortunately, the data was insufficient to draw any conclusions about its non Australian relatives. There is a strong superficial resemblance between the T. argutum species complex and the complex that includes T. japonicum, T. viscidium and T. stoloniferum. Members of this complex extend from India to Japan to Papua New Guinea. It is possible that T. argutum represents the southerly end of the continuum of variation in this group. Further investigation is needed.
In all analyses in which they were included, both Oncinocalyx betchei and Teucridium parvifolium fell firmly within Teucrium. In addition, the evidence suggests that they belong in section Teucrium. The cladistic morphological analysis places them on the well supported clade that includes the T. racemosum group as well as non Australian species of section Teucrium. The molecular data confirmed their relatedness to each and also suggested that an Australian species, T. species D, might be a close relative.
Future work should concentrate on obtaining more molecular data. Sequences from all Australian species and of likely close relatives, such as T. viscidium, would be invaluable in clarifying evolutionary relationships. They could also corroborate some of the conclusions made based on morphological data.