Quercus robur

Quercus robur or as it is known as English Oak or Pedunculate Oak is established and spreading in the range of Quercus garryana. Taxonomically Q. robur and Q. garryana are included in the same subgenus section Quercus the typical White Oaks. Many of the features of the White Oaks overlap creating uncertainty when identifying the taxa. and this oak is often mistaken for Q. garryana. The two species of oak can be differentiated by structure and canopy, bark color and texture, terminal bud size, texture, and color, and leaf outline and texture. Examples of these features are provided below with links to demonstrative observations. A well composed images of Q. garryana that demonstrate many of the Garry Oak features are at https://www.inaturalist.org/observations/26354578 and https://www.inaturalist.org/observations/26452037. A study of Q. robur is at https://www.inaturalist.org/observations/62889191.

Acorn Morphology
Although the western oaks of North America can be identified by many features. The acorn is one of the most reliable characteristics upon which to base an identity and is an epically important identifying feature of the White Oaks. Both Q. garryana and Q. robur have projections, tubercles, around the acorn involucre also known as a cap. There are distinctive fine scale differences. The involucre tubercles of Q. garryana project upwards like worts, creating a course and rough corky surface, an example is the second image at https://www.inaturalist.org/observations/14897334. Those of Q. robur are much less pronounced with a finely textured, egg-shale, surface and a velvety or pubescent feel see https://www.inaturalist.org/observations/59800624.
Additionally the acorn is morphologically different from Q. garryana. The Q. robur acorn is generally smaller and long and narrow. Observation https://www.inaturalist.org/observations/29658213 and https://www.inaturalist.org/observations/66249002 demonstrate the longer acorn. Limited measurements of the nut are one inch or slightly more long and half of an inch in diameter. The Q. garryana acorn is larger with a general rotund width and equal length. An example may be viewed at https://www.inaturalist.org/observations/59086474.
Q. robur is known as Pedunculate Oak from the distinctive arrangement of the acorns as the acorns are located at a distance from the terminal branch on a long thin stem, a peduncle, of the inflorescence, where the western White Oak acorns are sessile on the terminal branch. This character may be seen at https://www.inaturalist.org/observations/15794419. Other Eurasian oaks are pedunculate, however this feature identifies the observation as Q. robur in western North America.

Observational Survey
A survey of Q. robur acorns may be viewed at https://www.inaturalist.org/observations?place_id=97394&subview=grid&taxon_id=56133&term_id=12&term_value_id=14
and Q. garryana at https://www.inaturalist.org/observations?page=2&place_id=97394&subview=grid&taxon_id=68632&term_id=12&term_value_id=14. The survey of Q. robur suggests that some specimen have an outline that is similar to Q. garryana. However the scale is and size are unknown.

Leaf Morphology
The leaves of the western White Oak require study to differentiate from each other. Within each of the native oak species there is notable differences within each taxa. These may be the result of local environmental differences. Observation https://www.inaturalist.org/observations/48569644 located in a hot dry canyon on the east slope of the Cascade Range demonstrates a reduced somewhat skeletal leaf with deep sinuses. This leaf form contrasts with the fuller rounder leaf typically found west of the Cascades. This reduced form is also known from the interior Coast Range of Northern California. The Oregon White Oaks found west of the Cascades contrasts with a typically fuller rounder leaf https://www.inaturalist.org/observations/17148774.
The leaf base in 48569644 is a typical attenuate shape although the leaf base may also be rounded.
Q. garryana has a subtle feature that is quite distinctive, the secondary lobes. Observation https://www.inaturalist.org/observations/17148774 demonstrates this characteristic. These lobes are best defined by the leaf veins. The primary lobe ends with a secondary vein that branches from the primary vein, the vein that extends from the petiole to the distal tip. The secondary lobes end with a vein that branches from a secondary vein. Thus the secondary lobe is a smaller part of the primary lobe. In Q. garryana this secondary lobes is nearly always present, although it may be reduced in size.
Q. robur has a number of subtle features that can help separate the two species. A leaf base feature that is cited as a defining character is an auriculate or ear-lobed base. See observation https://www.inaturalist.org/observations/21205987. However this feature may not be present or evident. The leaf petiole is distinctive as it is very short or sessile. Observation https://www.inaturalist.org/observations/29150150 features this type of petiole. Note that the leaf bases appear to be directly attached to the terminal bud. A secondary lobe is almost never present in English Oak.

Leaf Out-line
The complexity of the oak leaf is somewhat confusing as a result of the sinuses and lobes. This requires a mental exercise of tracing the outline without the sinuses or tracing the outline on paper from lobe tip to lobe tip. Q. garryana has a wide ovate-elliptical shape with the mid point near the primary axis center. The Q. robur outline is a narrow elliptical-spathulate shape with the mid point shifted to the distal end and that can be described as obovate. Examples are found at https://www.inaturalist.org/observations/67559067, the leaf in this observation lacks the auriculate leaf base and has an attenuate base and https://www.inaturalist.org/observations/57576022.
Leaf Margin

Twig Morphology
The twigs of Q. garryana and Q. robur are notably different. The Oregon Oak twig is relatively thick and robust where English Oak is gracile. Q. garryana twig structure may be viewed at https://www.inaturalist.org/observations/68460125 and the forth image at https://www.inaturalist.org/observations/59086474. Q. robur at https://www.inaturalist.org/observations/67242689, https://www.inaturalist.org/observations/66113334, https://www.inaturalist.org/observations/56478757, and https://www.inaturalist.org/observations/69049811.

Terminal Bud Morphology
The buds are one of the most reliable features to differentiate the two oaks. The buds in both oaks change over the seasons, in summer they are smaller and enlarging through fall and winter.
The large pubescent terminal buds of Oregon Oak are distinctive from English Oak which are small and glabrous. The terminal buds in Q. robur are small round or oval and glabrous the second image in https://www.inaturalist.org/observations/67242689. Summer buds are green and winter buds before spring brake are reddish-chestnut. The buds in Q. garryana are large robust conical with dense rusty hair. Observation https://www.inaturalist.org/observations/68382945 captures the size and shape of the winter bud. Here the summer hair color has weathered to a gray and the bud scales have also darkened.

Trunk and Canopy
Canopy Structure
There is considerable variance in the canopy structure Q. robur generally it is a thick dense closed canopy but some trees demonstrate a more open structure. Various canopies may be viewed at https://www.inaturalist.org/observations/67157548

Bark
The texture and color of the bark of Q. robur and Q. garryana are different. These are best understood by direct observation to understand the features.

Q. garryana has a thick bark with rows of plates more or less in rows and separated by deep narrow furrows, the color is light gray. Observation https://www.inaturalist.org/observations/68385474 captures the typical aspect.
Q. robur bark has a thinner bark the ridges are smaller and light gray, the furrows are shallow and reddish brown in the shallow bottom. Observations https://www.inaturalist.org/observations/15905062 and https://www.inaturalist.org/observations/61817291 demonstrate. The bark in saplings and small diameter trees has a cherry bark like banding, observation https://www.inaturalist.org/observations/39216186.

Morphological Range
Q. robur has a extensive range in the palearctic region. It appears that the morphology of the taxa may also reflect that range and that regional characters. The comparison between native and introduced oak in the Pacific West Coast region requires consideration of the origin of the Eurasian oak. There are observations that suggest grater variance then suggested. It is likely that addational features require consideration based to the origin and variance of this oak. Thus origin may influence the features under review and this should be considered.

Other taxa of Eurasian Quercus with pedunculate infloresences are known which suggests a need to examine the North American observations of Q. robur to determine if there is other taxa with these features that are being misapplied. Wikipedia https://en.wikipedia.org/wiki/Quercus_robur reports the existence of synonyms, hybrids, and horticultural cultivars. This comparison is a consideration to separate Q. robur from Q. garryana within the range of Q. garryana.

Publicado el febrero 25, 2021 11:54 TARDE por carexobnupta