The guide told us about three varieties of the Art Nouveau style. Wikipedia has a different view, but I’m going to use the guide’s designations.
Copied from latvia.eu:
“Regular rhythms with a saturated surface décor define Eclectic Art Nouveau. Tensely articulated lines, geometric figures or stylized ornaments depicting plants, and masks, and extended proportions appeared in the early stages of Art Nouveau development.
“Perpendicular Art Nouveau spread after 1906 when romantic stylized motifs slowly disappeared from building facades. Vertical elements were emphasized in the facade. Bay windows and reliefs were strongly articulated and outwardly projecting strips extend upward for several floors. Ornamental decorations are introduced in the spaces between floors and are completely integrated into the basic architectural forms of the facade.
“National Romanticism reflects an attempt by Rîga architects to develop a distinctive Latvian style. This trend prospered between 1905 and 1911. Traditional wooden buildings and the decorative arts served as the main source of inspiration. Latvian architects embraced natural and local building materials.”