Drosophyllum is a genus with only one species, D. lusitanicum, which until recently belonged to the sundew family (Droseraceae), but since 2009 has been given its own family, Drosophyllaceae, Darwin assigned it to carnivorous plants in 1875. Common names are Portuguese sundew or dewy pine.  Drosophyllum is a perennial with a woody base. The stems quickly become creeping and in nature can reach a length of 1½ m. The close-fitting screw-set leaves do not fall off after wilting. During growth, as in Byblis, the leaves are rolled back, i.e. the upper side of the leaves faces outwards in the young clockwork-like leaf tip, which is the opposite of the situation in ferns and otherwise unknown from other plants. The linear leaves are provided with 4 rows of close-set, stalked and slime-secreting tentacles, which serve to passively capture primarily insects.

Below you can read about the following four topics:


Trap construction

Tentacles and glands



Drosophyllum is found in Portugal, southernmost Spain around Gibraltar and northernmost Morocco. It often grows near the coast on calcareous rocky soil and usually on drier soil than most carnivorous plants.

The construction and function of the trap

     The leaves are equipped with slime-secreting tentacles, which, unlike glandular hairs, are not only formed from epidermal cells, but also contain conductive tissue connected to the leaf’s vascular strands. The tentacles are closely spaced in 4 rows with 2 rows on the underside and one row on each of the edges of the linear leaf. The location on the underside is advantageous, as the underside faces away from the axis of the plant, so that the glands are exposed to the outside world. The tentacles secrete a sticky and elastic slime/mucus that contains gluconic acid, galactose, arabinose and more. When the wind blows the leaves together, the slime is drawn out in long threads between the leaves, forming a network that works similar to a spider’s web.

    When an insect struggles to free itself from the slime threads, the threads burst and pull the insect onto the leaf, where the prey inevitably comes into contact with several slime-covered tentacles. This capture method is called passive, as no movement caused by the plant is included in the capture process. The trap thus acts as a glue stick. The entire plant emits a sweet scent that can help lure prey to the traps. It cannot be ruled out that the glint of sunlight in the slime droplets and the red tentacle heads can also be attractive to certain insects. The picture above shows a cross-section of a young leaf with stalked tentacles and sessile digestive glands during development on the underside of the leaf.

Tentacles and digestive glands

     The tentacles are built like sundew (Drosera). They consist of a stalk and a head separated by a layer of endodermoid cells that control transport between the stalk and the head’s two layers of glandular cells. In the pictures in the middle and at right, the cell walls between the endodermoid cells appear without a red color because the cavities between the cellulose fibrils of the wall are filled with lipids. Thereby, all transport between stem and gland cells is forced through the endodermoid cells, where the cell membrane controls which substances can pass. In the same two images, water-conducting tracheids can be seen in the center of the stem. The ring-shaped stiffening thickenings of the cell wall resemble ladder rungs in the longitudinal section of the tentacle. From the mitosis in the figure on the left (telophase, red oval) it appears that the inner layer of glandular cells and the endodermoid layer have a common origin. The slime-producing gland cells are plasma-rich with large cell nuclei. The slime is produced in dictyosomes (see under Byblis- Danish page) primarily in the outermost layer of glandular cells, where the number of dictyosomes is 5 times greater than in the inner layer. If the water supply is blocked in Drosophyllum, the secretion stops immediately, but since new vesicles continue to be detached from the dictyosomes, the water supply is considered to be especially important for the maturation of the vesicles. If, on the other hand, the energy supply is blocked, the plasma is quickly emptied of vesicles, as no new formation takes place. The secretion rate is highly temperature dependent and reaches its maximum at 32℃. A dictyosomal vesicle then lives approx. 2½ minute.

     The digestive glands are created solely from epidermal cells. They consist of two layers of glandular cells separated from the leaf flesh by an endodermoid cell layer (black in the figure, right). The gland cells are so-called transfer cells with enlarged inner wall surface and that increases the cell membrane.

     When the digestive glands are matured approx. 2.5 cm from the leaf tip, perforations occur in the cuticle so that enzymes can pass out and nutrients in. The figure above shows absorption of the dye neutral red. At left is the leaf so young that only neutral red is absorbed in the tentacles. In the middle, the transition to functioning digestive glands is seen, and at right the fully grown leaf is seen, where all the digestive glands have perforated cuticle and can thus absorb the dye and nutrients.

     As in the other genera of glue-sticks, the digestive glands must be stimulated with nitrogenous secretions from the prey before the secretion of enzymes begins. The enzymes are stored in vacuoles and the walls of the transfer cells. When the gland is stimulated, the enzymes are washed out by a flow of water that results from the labyrinth walls being partially broken down, and the carbohydrates released thereby are probably used to establish an osmotic gradient that can drive the water flow through the activated gland. A prey struggling to break free also stimulates the slime-secreting glands to increase secretion. The enzymes work quickly, so a mosquito will normally be digested in approx. one day. The amount of digestive fluid that is secreted corresponds in the figure above to the area with black spots surrounding the dissolved prey. The secretion and absorption of the nutrients has been so energy-demanding that the glands (black) then die. Nutrient absorption takes place according to the same principle as described for Dionaea.

Flower and fruit

     The yellow flowers are 5-numbered with up to 25 mm long petals. They only open in full sunlight. Flowering occurs in the spring. The flower stalk and sepals are also provided with tentacles, but there are no digestive glands. It is therefore assumed that the tentacles here primarily have a defensive function. The fruit is a capsule that opens by longitudinal fissures. The black pear-shaped seeds ripen in a few weeks. Note that the flowers sit between the sticky leaves and not raised high above them, as is generally the case with carnivorous plants. Thus, in Drosophyllum and similarly in Byblis, the flower can help to lure prey into the traps.

The following book serves extensiv knowledge on carnivorous plants:
Juniper B.E., Robbins R.J. & Joel D.M. 1989. The carnivorous plants. Academic Press. 353 pp.

H. S. Heide-Jørgensen, November 2020, translated April 2024.

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