Aromatic compounds in some species of leucas r.br. (labiatae): with 2 tables (Labiatae)

Monoterpenoids were principal compounds found in leaves and inflorescences of four species of Leucas R.BR, of the aromatic family Labiatae (or Lamia‐ceae). Leaves of three species of the genus, namely L. aspera SPRENG., L. lavandulifolia REES and L. stricta BENTH., contained greater number of monoterpenoids than their inflorescences. The different physiological states of the leaves and the inflorescences were suggested to be the reasons behind this difference in contents. The species L. cephalotes (ROTH) SPRENG., however, possessed higher number of terpenoids in the inflorescence than in its leaves. The green and leafy nature of bracts around flowers of this species was thought to be one of its causes. In all the four species, altogether nine terpenoids were recorded, of which acylic monoterpenoids (citral, citronellal linalool and linalyl acetate) were higher in number than monocyclic (α‐terpineol and thymol) and bicyclic (α‐β‐thujone and borneol) ones. The only triterpenoid identified was ß‐sitosterol. The genus Leucas was considered primitive because of its preference for the simplest type of monoterpenoids, that is, acyclic ones. Terpenoids of the genus were investigated for the first time. Linalool, an acyclic monoterpenoid, was thought to be the initial compound from which other monoterpenoids might have been derived. The three species contained either α‐β‐thujone or borneol, except L. stricta which lacked both. On the basis of the findings, the following genetic constitutions, in respect to the two compounds, were suggested for the species: L. aspera ‐ Thu + Bor − , L. lavandulifolia and L. cephalotes ‐ Thu − Bor + and L. stricta ‐ Thu − Bor − . A cross between species Thu + Bor − and Thu − Bor + , leading to a progeny with an expected genetic constitution Thu + Bor + , may throw light on the behaviour of genes responsible for the two compounds. Since α‐β‐thujone is chemically a simpler terpenoid than borneol, the species containing the former was considered to be evolutionarily primitive and the ones containing the latter a bit advanced. Camphor and 1,8‐cineole were absent from all the four species. In α‐terpineol containing species of Leucas gene/s responsible for α‐terpineol → 1,8‐cineole isomerization reaction was thought to be altogether absent. An aromatic phenol, eugenol, was observed in the leaves of only two species, L. aspera and L. stricta. The genus was suggested to posses synthetic pathways both for terpenoid and phenol.