Lithium equivalent width (EW, in Å) versus the spectral type for different sets of spectroscopically confirmed members of Collinder 69. Top: new members reported in this work where accretors (based on the Hα emission, see Paper II for details) are highlighted in red, and class II sources (based on IRAC data, see Barrado y Navascués et al. 2007 and Paper II) and spectroscopic binaries (from Sacco et al. 2008 and Maxted et al. 2008) are surrounded by open circles and squares, respectively. Middle: new members are shown as filled black circles, while members from the literature (Dolan & Mathieu 1999, 2001; Barrado y Navascués et al. 2004b, 2007) are shown as smaller grey circles. Bottom: comparison of Collinder 69 members (joining the samples from the middle panel), displayed as filled black dots, with Sigma Orionis low mass stars from Zapatero Osorio et al. (2002), represented with star symbols. In all the panels, the solid line traces the upper envelope of the values measured in older clusters such as IC 2391, IC 2602, the Pleiades, and M 35; and the short-dashed blue lines corresponds to the cosmic abundances – A(Li) = 3.1 – from gravities of log    g = 4.5 and 4.0, respectively (curves of growth from Zapatero Osorio et al. 2002).