Carex pilulifera, the pill sedge,<ref name=BSBI07>Template:Cite web</ref> is a European species of sedge found in acid heaths, woods and grassland from Macaronesia to Scandinavia. It grows up to Template:Convert tall, with 2–4 female spikes and 1 male spike in an inflorescence. These stalks bend as the seeds ripen, and the seeds are collected and dispersed by ants of the species Myrmica ruginodis.
The culms of Carex pilulifera grow to a length of Template:Convert, and are often noticeably curved.<ref name="Jermy">Template:Cite book</ref> The leaves are Template:Convert long and Template:Convert wide, and are fairly flat.<ref name="Jermy"/> The rhizomes of C. pilulifera are very short, giving the plant a caespitose (densely tufted) appearance.<ref name="Jermy"/> The tussock grows outwards through the production of annual side-shoots.<ref name="Kjellson"/>
The inflorescence comprises a single, terminal, male (staminate) spike, and 2–4 lateral female (pistillate) spikes.<ref name="Jermy"/> The spikes are clustered together, and the whole inflorescence is Template:Convert long.<ref name="Jermy"/> The female spikes are Template:Convert long, ovoid or approaching spherical,<ref name="Jermy"/> and contains 5–15 flowers.<ref name="Kjellson"/> The female spikes are attached directly to the stem, and each is subtended by a bract which does not form a sheath.<ref name="Jermy"/> The male spike is Template:Convert long and much narrower.<ref name="Jermy"/>
Distribution and ecology
Carex pilulifera has a wide distribution in Europe, extending from Macaronesia and the Balkan Peninsula to Scandinavia.<ref name="FE">Template:Cite book</ref> It grows on acidic substrates including heathland, grassland and woodland.<ref name="Kjellson"/> It typically inhabits soils with a pH of 4.5–6.0.<ref name="Jermy"/>
As the seeds of C. pilulifera ripen, the culms bend, and can eventually touch the ground.<ref name="Kjellson">Template:Cite journal</ref> The seeds are then dispersed by ants, particularly Myrmica ruginodis,<ref name="Kjellson"/> in a process known as myrmecochory, and are eaten by other insects, such as the ground beetle Harpalus fuliginosus.<ref name="Kjellson"/>
Carex pilulifera was described by Carl Linnaeus in his 1753 work Species Plantarum, which marks the starting point of botanical nomenclature.<ref name="FE"/> The specific epithet Template:Lang means "bearing small globular structures", in reference to the female spikes.<ref>Template:Cite web</ref>