Klobuk je 5-12 cm širok i manje ili više mesnat. U mladosti je konveksan, a kasnije postaje ulegnut kao lijevak i poprima narančastocrvenu boju. Jasno su vidljivi koncentrični krugovi, koji, kada gljiva ostari, postanu zelene mrlje. Tada se rub uvrne, a klobuk postanje mazav. Listići su gusti, narančaste boje, a kada ih se pritisne, postanu zelenkasti. Stručak je 3-8 cm visok, cilindričnog oblika, a na dnu je malo tanji. Narančaste je boje. Pun je dok je gljiva mlada, ali postane šupalj kada ostari. Meso je vrlo ugodnog mirisa
Spore su eliptičnog oblika, smeđe boje, veličine 7-9x6-7 µm.
Rujnicu je moguće zamijeniti sa nekoliko sličnih, ali jestivih vrsta. Također je moguća zamjena sa brezovkom (Lactarius torminosus), koja je otrovna, ali koja raste ispod breza i ima dlake na cijelom klobuku.
Ova gljiva je izvorno rasla u južnim Pirinejima, ali je sada uvezena u druge zemlje. Raste od ljeta do kraja jeseni u zimzelenim šumama, a posebno ispod borova, na vlažnim travnjacima i pored šuma.

Lactarius deliciosus, commonly known as the Saffron milk cap, Red pine mushroom, is one of the best known members of the large milk-cap genus Lactarius in the order Russulales. It is found in Europe and North America and has been accidentally introduced to other countries under conifers and can be found growing in pine plantations.
A fresco in the Roman town of Herculaneum appears to depict Lactarius deliciosus and is one of the earliest pieces of art to illustrate a fungus.
When grown in liquid culture, the mycelium of this fungus produces a mixture of fatty acids and various compounds such as chroman-4-one, Anofinic acid, 3-hydroxyacetylindole, ergosterol, and cyclic dipeptides.
Lactarius deliciosus has a carrot orange cap which is convex to vase shaped, inrolled when young, 4 to 14 cm (1.5–7 in) across, often with darker orange lines in the form of concentric circles. The cap is sticky and viscid when wet, but is often dry. It has crowded decurrent gills and a squat orange stipe which is often hollow, 3 to 8 cm (1–3 in) long and 1 to 2 cm (0.4–0.8 in) thick. This mushroom stains a deep green color when handled. When fresh, the mushroom exudes an orange-red latex or "milk" that does not change color.
In North America, this mushroom is often confused with Lactarius rubrilacteus which stains blue, exudes a red latex, and is also edible.
Lactarius deliciosus grows under the acidic soil of conifers and forms a mycorrhizal relationship with its host tree. It is native to the southern Pyrenees where it grows under Mediterranean pines. Both this fungus and L. deterrimus are collected and sold in the İzmir Province of southwestern Turkey, and the Antalya Province of the south coast.
It can also be found in woodlands in North America as well as having been introduced to Chile, Australia and New Zealand, where it grows in Pinus radiata plantations. A very popular place for collecting this mushroom, especially among the Polish community, is in the Oberon area in New South Wales, Australia, where they can grow to the size of a dinner plate. Many people of Italian, Polish, Ukrainian and other eastern European ancestry in the states of Victoria and New South Wales, Australia travel to collect these mushrooms after autumn rainfall around Easter time. In Cyprus it is found in the pine forests where many people "hunt" them with vigour. It is considered as one of the local delicacies.
Lactarius deliciosus is a widely collected mushroom in the Southern Pyrenees and Majorca and used in Valencian and Catalan cuisine. One recipe recommends they should be lightly washed, fried whole cap down in olive oil with a small amount of garlic and served drenched in raw olive oil and parsley. The same recipe advised that butter should never be used when cooking this mushroom.
Further north and east it is a feature of Provençal cuisine.
They are also collected in Poland, where they are traditionally served fried in butter, with cream, or marinated.
They are also very known in Cyprus, where they are usually cooked on charcoal and marinated with olive oil and lemon, or fried with onions with red wine.
In some older guides, the saffron milk cap is considered an excellent mushroom, having 'a crisp texture'. In fact, when naming the mushroom (deliciosus = delicious), the mycologist had mistaken the mushroom with Lactarius sanguifluus, which is an excellent, pleasantly crunchy mushroom. Today, most mycologists hold Lactarius sanguifluus in higher esteem than its pretender, Lactarius deliciosus.