Sensu - Examples in Practical Taxonomy

Examples in Practical Taxonomy

Sensu is used in the taxonomy of living creatures to specify which circumscription of a given taxon is meant, where more than one circumscription can be defined.

Examples:

• "The family Malvaceae s.s. is cladistically monophyletic."

This means more or less that the members of the entire family of plants going under the name Malvaceae, (strictly speaking), which comprises over 1000 species, including the closest relatives of cotton and hibiscus, all descend from a shared ancestor, specifically, that they shared a most recent common ancestor (MRCA). That ancestor might have been a single species of plant, or even possibly a single individual plant. Conversely it also means that the family includes all the descendants of that ancestor. Other species of plants that some people might (broadly speaking or s.l.) have included in the family would not have shared that MRCA (or they too would hve been members of the family Malvaceae s.s. In short, the circumscription s.s. includes all and only plants that have descended from that particular ancestral stock.

• "In the broader APG circumscription the family Malvaceae s.l. includes Malvaceae s.s. and also the families Bombacaceae, Sterculiaceae and Tiliaceae."

Here the circumscription is broader, stripped of some of its constraints by saying sensu lato; that is what speaking more broadly amounts to. In this example, by adding other groups of plants to the family Malvaceae s.l., including those related to cacao, cola, durian, and jute, the circumscription omits some of the criteria by which the new members previously had been excluded. Now it is no longer clear that all members of the circumscription descended from that one ancestor. Consequently, we say that Malvaceae s.l. form a polyphyletic group, one that does not share any single ancestor that had no other descendants. Then their most recent common ancestor could have lived perhaps tens of millions of years earlier than the most recent common ancestor of the Malvaceae s.s. alone; also there may be other extant species that are not included in the modern Malvaceae s.l..

• "The 'clearly non-monophyletic' series Cyrtostylis sensu A.S. George has been virtually dismantled..."

This specifies Alex George's particular description of that series. This is a different kind of circumscription; it does not refer directly to the biological nature of the common features of the plants, but to the fact that A.S. George referred to them as a series. "Sensu A.S. George" means that A.S. George discussed the Cyrtostylis in that series, and that members of that series are the ones under discussion in the same sense, — how A. S. George saw them. The current author might or might not approve George's circumscription, but George's is the circumscription currently under consideration.