Geranium robertianum – Herb robert

This is an annual or sometimes biennial semi – rosette plant in Geraniaceae family, with red, pink or white flowers. This is a very common species found in a great variety of habitats. The floral formula is: 5S; 5P; 5+5 St (C5) for 5 sepals, 5 petals, 10 stamens in two whorls and 5 fused carpels.

Floral buds are collected and immediately fixed in FAA and prepared for paraffin embedding. Successive cross sections 8 μm thick are made to describe the organization of the
floral parts at 8 different levels of the bud. Sections stained with safranin – alcian blue have been photographed with Color Digital Camera Leica DC 300F mounted on a microscope Leica DMI RE2. Below microphotographs of a few of the sections for which description is given.

1. Stigmal level
2. Stigma level: From outside of the section toward inside or center we successively find the 5 sepals, 5 petals, 5 anthers of stamens and in the middle the style. Filaments of the 5 other stamens are seen as small cross sections between sepals and petals.
3. Androecium (stamens) and gynoecium (carpels): S1 à S5: 5 sepals; P1 à P5: 5 petals; 1 à 5: anthers of 5 stamens; 6 à 10: filaments of 5 stamens. Center: 5 fused carpels
Part of stamen showing anther with 4 pollen sacs containing pollen grains (g) stained red. ep: epidermis; red arrow: mechanical layer; pa: parenchyma
4. Gynoecium in the center of the section: S: sepals; P: petals; 1 to 10: filaments of 10 stamens; Center: 5 chambers with 1 to 2 ovules per chamber.
Higher magnification view of 5 ovarian chambers (1 to 5) with 1 or 2 ovules per chamber. Red arrow: carpels fused at this level of the section
5. Bud base: S: sepals; P: petals fused at this level of the section. Arrows: vascular bundles (1 to 5)
6. Floral peduncle: 1 à 5: 5 vascular bundles. The peduncle is limited by an epidermis with some trichomes.