Final answer:
Charophyte algae lack the alternation of multicellular generations, a characteristic seen in land plants. They share many other features with land plants, including the presence of chlorophyll a and b, and cellulose in their cell walls.
Step-by-step explanation:
The characteristic that is absent in charophyte algae, when compared to their closest relatives, land plants, is the alternation of multicellular generations. Charophytes share many features with land plants, such as having chlorophyll a and b in their chloroplasts and cellulose within their cell walls. They also form a cell plate during cytokinesis through a structure called phragmoplast, and they feature intercellular channels called plasmodesmata. However, unlike land plants, charophytes do not exhibit alternation of generations, which is the process where plants alternate between two multicellular stages: the haploid gametophyte and the diploid sporophyte.