Fig. 2.

Transverse light microscope sections of Impatiens showing variation in wood development at the base of the stem. (A) Impatiens mansonii, clearly herbaceous stem without wood cylinder, intrafascicular cambium produces few wood cells (arrows). (B) Impatiens cf. stuhlmannii, herbaceous stem with narrow wood cylinder; character state after gap weighting = 2. (C) Impatiens hawkeri, herbaceous stem with slightly larger wood cylinder, character state after gap weighting = 4. (D) Impatiens latifolia, herbaceous stem with the most developed wood cylinder observed, but still limited compared with the entire stem diameter; character state after gap weighting = 9. (E) Impatiens eubotrya, woody stem, ratio of double wood cylinder thickness over stem diameter is significantly larger than in (D); wood cylinder also extends to the upper parts of the stem; character state after gap weighting = 14. (F) Impatiens gesneroidea, clearly woody stem; character state after gap weighting = 23.