Ranunculus aquatilis [Water Crowfoot]

[nfoto]

Rørslett, B., 2014. Ranunculus aquatilis L. s.lat. (Ranunculaceae). Water Crowfoot. Flowers photographed in visible and ultraviolet light. http://www.ultraviol...water-crowfoot/

 

Ranunculus aquatilis L. s.lat.

(incl. Ranunculus peltatus Schrank, excl. Ranunculus baudoti Godr.)

Syn. Ranunculus heterophyllus Weber; Batrachium radians (Revel) Dumort.; Batrachium aquatilis (L.) Dumort.; Ranunculus diversifolius Gilib.; Ranunculus capillaceus Thuill.; Batrachium gilibertii V.I.Krecz.; Ranunculus godronii Gren.; Ranunculus radians Revel; Ranunculus peltatus Schrank; Ranunculus aquatilis L. subsp. peltatus (Schrank) Syme; Batrachium aquatile (L.) Dumort. var. peltatum (Schrank) Dumort., Batrachium peltatum (Schrank) Petrovsky ; Batrachium floribundum Dumort.; Ranunculus penicillatus (Dumort.) Bab. subsp. pseudofluitans (Syme) S.D.Webster; Ranunculus fluitans auct.

 

NO: Storvass-soleie; kystvass-soleie

SE: Skjöldmöja

DK: Storblomstret Vandranunkel

FI: Järvisätkin

DE: Wasser-Hahnenfuß

EN: [Pond] Water Crowfoot

 

This is a species complex that has bewildered and confused botanists for centuries since C. Linnaeus first described the aquatic, white-flowered Ranunculus aquatilis in 1753. Part of the confusion and nomenclature issues is the fact that like most aquatic plants, R. aquatilis shows a strong plasticity in its growth appearance. This reflects its adaptation to local aquatic environmental conditions. Thus, floating leaves may or may not develop, the finely dissected underwater foliage may be rigid or lax (then plants often interpreted as R. penicillatus or R. 'fluitans'), flowers may have overlapping or widely separated petals, and so on. It is noteworthy that a population may commence the flowering stage by showing small flowers having overlapping petals, later to become much bigger and now with petals widely separated. In 2014, I studied such populations in a small Norwegian river and am convinced the plants despite a greatly changing appearance over the season all belong to the same taxon. Such seasonal variability makes the botanists' attempts to put this taxon into clear-cut categories even more difficult of course, in particular if the phenomenon is not sufficiently know to them.

 

Some authors prefer the aquatic Ranunculus spp. to be treated as a separate genus, Batrachium. I remain unconvinced this is required and in fact, moving these taxa over to another genus only serves to exacerbate the existing nightmare of nomenclature issues, so any clarity gained on the genus level certainly is lost in the ensuring nomenclature mess.

 

The water crowfoot is widely distributed in Europe to become less common towards the high North. It occurs in various kinds of rivers, from small to big and can tolerate quite strong currents. As nutrient uptake and gas exchange are facilitated by the dissected specialised submersed leaves, plus the rhizome and roots are active in acquiring nutrients, R. aquatilis can occur over a wide range of trophic states, from near oligotrophic rivers to meso- or eutrophic lakes.

 

Flowers develop from May to September. The flowers are borne on long branches from a floating stem and are eagerly visited by smaller pollinators. Each flower has a limited longevity and sheds their petals easily when impacted by wind or waves. When the plants occur in stagnant water, floating leaves may be more commonly seen than in swift-flowing habitats. In larger lakes, such as the Norwegian lakes Tyrifjord and Randsfjord, most or all individuals may be present in a prostrate sterile form in deep water. Here only underwater foliage is present and the creeping rhizome can be several meters long.

 

Material collected and photographed from Himdalen, Fet municipality, Norway, June-July 2014. In this small river, stands of R. aquatilis develop profusely during summer to nearly choke river flow.

 

Image reference: RANU_AQU_B1407051617_VIS.jpg

 

The shiny white petals (or technically, honey leaves) have a large basal yellow patch. The rounded or moon-crescent nectaria are located in the middle of this yellow mark. In the photograph below, a small insect is visiting a nectary.

 

Image reference: RANU_AQU_B1407051614_VIS.jpg

 

All visible light photographs: Nikon Df, Voigtländer APO-Lanthar 125 mm f/2.5 lens, daylight

 

Frontal view of the flower in UV:

Image reference: RANU_AQU_I1407051977_UV.jpg

 

Rear view:

Image reference: RANU_AQU_I1407051976_UV_rear_view.jpg

 

In UV, the white section of the petals is rendered in a medium blue false colour indicating it is slightly reflective. The basal patch with the nectary is different and due to the presence of conical cells, can be either shiny UV "white" or near UV black depending on the directional nature of the UV light field. The close-ups conducted with a UV flash will indicate more of the highly reflective appearance because the light output is directional. It is noteworthy that the frontal and rear views of the flower show a different behaviour probably mediated by a greater development of conical cells on the front side.

 

When the light field is more diffusive, as under an overcast sky, the basal patches tend to take on more UV grey appearance. Do note the shredded petals are trapped within the dense stand and show up more reflective in UV than the flowers themselves.

 

Image reference: RANU_AQU_I1407051981_UV.jpg

 

All ultraviolet light photographs: Nikon D3200 (modified), UV-Nikkor 105 mm f/4.5 lens, internal Baader U2" (Venus) filter, SB-140 flash.

 

[Published 6 July 2014. Last updated 7 July 2014]

[msubees]

Beautiful flowers!

[Damon]

Pretty cool and good to see how you are using the terminology and what you are picking out as interesting/important. Nice shot especially the frontal UV.

 

Have you found that there are a decent amount of flowers that show something underneath? I suppose insects could be looking up at the flower at some point. Seems a tad odd though. Maybe just bleeding through from the top.

 

-D

[nfoto]

In UV, the underside of the flower structure sometimes is strikingly different from what is recorded normally. I think Andrea and I both have become aware of this phenomenon and thus try to include a rear view if possible. When there is a difference, the rear side tends to be rendered darker or having more prominently UV-darkened veins.

 

The aquatic Ranunculus spp. have prominent and easily accessible nectaria. See the illustration below. One observes smaller insects eagerly visiting these nectaria. Also note how the nectaria are embedded inbetween anthers and stigmas.