Editing Drosera (section)

=== Leaves and carnivory ===
[[File:Drosera capensis bend.JPG|thumb|upright|Leaf and tentacle movement on ''[[Drosera capensis|D. capensis]]'']]
Sundews are characterised by the glandular tentacles, topped with sticky secretions, that cover their [[Leaf|leaves]]. The trapping and digestion mechanism usually employs two types of glands: stalked glands that secrete sweet mucilage to attract and ensnare insects and enzymes to digest them, and [[Sessility (botany)|sessile]] [[gland]]s that absorb the resulting nutrient soup (the latter glands are missing in some species, such as ''[[Drosera erythrorhiza|D.&nbsp;erythrorhiza]]''). Small prey, mainly consisting of insects, are attracted by the sweet secretions of the peduncular glands. Upon touching these, the prey become entrapped by sticky mucilage which prevents their progress or escape. Eventually, the prey either succumb to death through exhaustion or through asphyxiation as the mucilage envelops them and clogs their [[Spiracle (arthropods)|spiracle]]s. Death usually occurs within 15 minutes.<ref name="Darwin-1875">{{cite book| author-first=Charles |author-last=Darwin | title=Insectivorous Plants
| year=1875| location=London|publisher= John Murray  |url=http://darwin-online.org.uk/EditorialIntroductions/Freeman_InsectivorousPlants.html |access-date= March 14, 2022}}</ref> The plant meanwhile secretes [[esterase]], [[peroxidase]], [[phosphatase]] and [[protease]] [[enzymes]].<ref name="Barthlott-2004" />{{rp|41}} These enzymes dissolve the insect and free the nutrients contained within it. This nutrient mixture is then absorbed through the leaf surfaces to be used by the rest of the plant.
 [[File:Drosera Glandular Hair.jpg|thumb|Drosera Glandular Hair]]                                                                                    
All species of sundew are able to move their tentacles in response to contact with edible prey. The tentacles are extremely sensitive and will bend toward the center of the leaf to bring the insect into contact with as many stalked glands as possible. According to [[Charles Darwin]], the contact of the legs of a small gnat with a single tentacle is enough to induce this response.<ref name="Darwin-1875"/> This response to touch is known as [[thigmonasty]], and is quite rapid in some species. The outer tentacles (recently coined as "snap-tentacles") of ''[[Drosera burmanni|D.&nbsp;burmanni]]'' and ''[[Drosera sessilifolia|D.&nbsp;sessilifolia]]'' can bend inwards toward prey in a matter of seconds after contact, while ''[[Drosera glanduligera|D.&nbsp;glanduligera]]'' is known to bend these tentacles in toward prey in tenths of a second.<ref>Hartmeyer, I. & Hartmeyer, S., (2005) Drosera glanduligera: Der Sonnentau mit "Schnapp-Tentakeln", DAS TAUBLATT (GFP) 2005/2: 34-38</ref> In addition to tentacle movement, some species are able to bend their leaves to various degrees to maximize contact with the prey. Of these, ''[[Drosera capensis|D.&nbsp;capensis]]'' exhibits what is probably the most dramatic movement, curling its leaf completely around prey in 30 minutes. Some species, such as ''[[Drosera filiformis|D.&nbsp;filiformis]]'', are unable to bend their leaves in response to prey.<ref name="D'Amato, Peter-1998">{{cite book | author=D'Amato, Peter | title=The Savage Garden: Cultivating Carnivorous Plants | publisher=Ten Speed Press | location=Berkeley, California | year=1998 | isbn=978-0-89815-915-8 | title-link=The Savage Garden: Cultivating Carnivorous Plants }}</ref>

[[File:DroseraIndicaEmergences.JPG|thumb|Emergences of an Australian ''[[Drosera indica|D. indica]]'']]
A further type of (mostly strong red and yellow) leaf coloration has recently been discovered in a few Australian species (''[[Drosera hartmeyerorum|D. hartmeyerorum]]'', ''[[Drosera indica|D. indica]]''). Their function is not known yet, although they may help in attracting prey.

The leaf morphology of the species within the genus is extremely varied, ranging from the sessile [[:File:Leaf morphology no title.png|ovate]] leaves of ''D. erythrorhiza'' to the bipinnately divided [[:File:Leaf morphology no title.png|acicular]] leaves of ''[[Drosera binata|D. binata]]''.

While the exact physiological mechanism of the sundew's carnivorous response is not yet known, some studies have begun to shed light on how the plant is able to move in response to mechanical and chemical stimulation to envelop and digest prey. Individual tentacles, when mechanically stimulated, fire action potentials that terminate near the base of the tentacle, resulting in rapid movement of the tentacle towards the center of the leaf.<ref>{{Cite journal|last1=Williams|first1=Stephen E.|last2=Pickard|first2=Barbara G.|date=1972|title=Receptor potentials and action potentials in Drosera tentacles|journal=Planta|volume=103|issue=3|pages=193–221|doi=10.1007/bf00386844|pmid=24481555|bibcode=1972Plant.103..193W |s2cid=2155695|issn=0032-0935}}</ref><ref name="Williams-1980">{{cite book |last1=Williams |first1=S. E. |last2=Pickard |first2=B. G. |chapter= The Role of Action Potentials in the Control of Capture Movements of Drosera and Dionaea|title= Plant Growth Substances 1979|series=Proceedings in Life Sciences |date=1980 |pages=470–480 |doi=10.1007/978-3-642-67720-5_48|isbn=978-3-642-67722-9 }}</ref> This response is more prominent when marginal tentacles further away from the leaf center are stimulated. The tentacle movement response is achieved through auxin-mediated [[acid growth]]. When action potentials reach their target cells, the plant hormone [[auxin]] causes protons (H<sup>+</sup> ions) to be pumped out of the plasma membrane into the cell wall, thereby reducing the pH and making the cell wall more acidic.<ref>{{Cite journal|last1=Rayle|first1=D. L.|last2=Cleland|first2=R. E.|date=1992-08-01|title=The Acid Growth Theory of auxin-induced cell elongation is alive and well.|journal=Plant Physiology|volume=99|issue=4|pages=1271–1274|doi=10.1104/pp.99.4.1271|issn=0032-0889|pmid=11537886|pmc=1080619}}</ref> The resulting reduction in pH causes the relaxation of the cell wall protein, expansin, and allows for an increase in cell volume via osmosis and turgor. As a result of differential cell growth rates, the sundew tentacles are able to achieve movement towards prey and the leaf center through the bending caused by expanding cells.<ref>{{Cite journal|last=Hooker|first=Henry D.|date=1917|title=Mechanics of Movement in Drosera rotundifolia|jstor=2479748|journal=Bulletin of the Torrey Botanical Club|volume=44|issue=8|pages=389–403|doi=10.2307/2479748}}</ref>  Among some ''Drosera'' species, a second bending response occurs in which non-local, distant tentacles bend towards prey as well as the bending of the entire leaf blade to maximize contact with prey. While mechanical stimulation is sufficient to achieve a localized tentacle bend response, both mechanical and chemical stimuli are required for the secondary bending response to occur.<ref>{{Cite journal|last1=Krausko|first1=Miroslav|last2=Perutka|first2=Zdeněk|last3=Šebela|first3=Marek|last4=Šamajová|first4=Olga|last5=Šamaj|first5=Jozef|last6=Novák|first6=Ondřej|last7=Pavlovič|first7=Andrej|date=March 2017|title=The role of electrical and jasmonate signalling in the recognition of captured prey in the carnivorous sundew plant Drosera capensis|journal=The New Phytologist|volume=213|issue=4|pages=1818–1835|doi=10.1111/nph.14352|issn=1469-8137|pmid=27933609|doi-access=free}}</ref>