So far, I have only found Xanthidium armatum in moors in Austria. This alga occurs very frequently there, sometimes in large quantities. Its approximately octagonal semi-cell with branched spines at each corner give it a distinctive appearance. In the center of each semi-cell there is also a ring of simple spines that looks like a crown. The spines are often yellowish, brownish, or orange-brown in color. The cell wall is covered with a pattern of fine pores. Each semi-cell is said to contain four chloroplasts, each with one pyrenoid (John et al., 2002). However, I have also observed semi-cells with more pyrenoids.