Pilosella officinarum [Mouse-ear Hawkweed]

[Andrea B.]

Blum, A.G. (2014) Pilosella officinarum F.W. Schultz & Sch. Bip. (Asteraceae) Mouse-ear Hawkweed. Flowers photographed in ultraviolet and visible light. http://www.ultraviol...e-ear-hawkweed/

 

Southwest Harbor, Mount Desert Island, Maine, USA

06 July 2014

Wildflower

 

Synonyms:

• Hieracium pilosella L.
  
• Mouse Ear
  

Comments:

The long-haired leaves, basal rosette, flowers growing singly and height less than a foot distinguish H. pilosella from its taller cousins. Another important detail for identification is the presence of glandular hairs on the involucre and upper peduncle.

 

As B. Rørslett has noted in a comment below, the Hieracium and Pilosella can be extraordinarily difficult to identify. However, the P. officinarum shown here fortunately hit all the marks of the Flora Novae Angliae key⁽²⁾. Some details of the identification are presented in the photos below.

 

The early summer blooming Mouse-ear Hawkweed is usually not found in flower after mid-July in Southwest Harbor although the basal leaf rosettes remain. The plants can form extensive colonies via their stolons.

 

In UV light the flower face exhibits a wide, somewhat diffuse UV-dark bullseye. The longer underlying rays are lighter, but not particularly UV-bright. The false colour yellow appears only on the face. The abaxial side of the rays shows some false blue streaks presenting an interesting contrast to the front. The curled ends of the UV-dark stigmas are covered in UV-bright pollen.

 

Reference:

1. New England Wild Flower Society (2014) Hieracium pilosella. Mouse-ear Hawkweed.

2. New England Wild Flower Society (2014) Hieracium Dichotomous Key.

3. Haines, A. (2011) Flora Novae Angliae: A Manual for the Identification of Native and Naturalized Higher Vascular Plants of New England, Yale University Press, New Haven, CT.

 

Equipment [Nikon D600-broadband + Novoflex 35mm f/3.5 Noflexar]

 

Visible Light [f/11 for 1/1.3" @ ISO 400 in Sunlight with Baader UVIR-Block Filter]

 

Visible Light [f/11 for 1/25" @ ISO 100 with onboard Flash and Baader UVIR-Block Filter]

Pollen-covered stigmas.

 

Visible Light [f/11 for 1/1.6" @ ISO 400 in Sunlight with Baader UVIR-Block Filter]

Side view of the capitula showing dense, dark hairs on the involucre.

 

Visible Light [Full-size extract from preceding photo]

Close-up of glandular hairs on the involucre.

 

Visible Light [Full-size extract from preceding photo]

Close-up of glandular hairs on the stem area nearest the involucre.

 

Ultraviolet Light [f/11 for 15" @ ISO 400 with SB-14 UV-modified Flash and Baader UV-Pass Filter]

Wide, UV-dark central bullseye with the longest underlying rays much more UV-reflective.

The pollen on the UV-dark stigmas is very UV-reflective.

A long exposure was made in order to use the UF flash twice.

 

Ultraviolet Light [f/11 for 15" @ ISO 400 with SB-14 UV-modified Flash and Baader UV-Pass Filter]

The bullseye appears more diffuse in this angled view of the flower.

A long exposure was made in order to use the UF flash twice.

 

Ultraviolet Light [f/11 for 15" @ ISO 400 with SB-14 UV-modified Flash and Baader UV-Pass Filter]

Mottled blue false colour on the abaxial side of the capitulum.

A long exposure was made in order to use the UF flash twice.

 

Infrared Light [f/11 for 2.5" @ ISO 400 in Sunlight with B+W 093 IR-Pass Filter]

Very IR-reflective rays.

 

Infrared Light [f/11 for 2" @ ISO 400 in Sunlight with B+W 093 IR-Pass Filter]

IR-dark involucre hairs.

 

Visible Light [f/11 for 1" @ ISO 400 in Sunlight with Baader UVIR-Block Filter]

Leaf top - a few scattered long hairs.

 

Visible Light [f/11 for 1/1.6" @ ISO 400 in Sunlight with Baader UVIR-Block Filter]

Leaf bottom - very hairy with a mix of compound and long hairs.

 

Visible Light [Full-size extract from preceding photo]

Contrast enhanced close-up of abaxial stellate leaf hairs.

 

Visible Light [f/11 for 1/1.3" @ ISO 400 in Sunlight with Baader UVIR-Block Filter]

Leaf side view showing the long hairs.

[nfoto]

Even after being split off from the infamous Hieracium, the Pilosella species are a nightmare to identify. They occupy page after page in the European floras. Talented botanists over the centuries have been mired in these genera, and the nomenclature and type specification may be questionable.

 

A basic problem is they are not 'Linnean' species, rather nodes in an interconnected network of mutations and phenotype plasticity. Some of the Pilosella may have a sexual propagation and thus add to the overall variability and speciation by hybridisation.

[Andrea B.]

It may be because these Pilosella are on an Island and have less chance to mix or drift, but these P. officinarum are easily identified from the Flora Novae Angliae key. My specimen here hit all the marks on the key.

 

However, for other Hieracium here I cannot say the same. They can be indeed a nightmare to ID.

 

The Flora Novae Angliae mentions the Hieracium/Pilosella split but has refrained from incorporating it until the Hieracium/Stenotheca problems are resolved. However, I choose to list my flowers as Pilosella.