Resting No Longer, It's Spring!

Some Primula species spend the winter as conspicuous, above ground resting buds. The mature leaves die back in autumn and a new set of short leaves called bud-scales are grown closely together to form a protective layer around the growth point. These bud-scales are modified leaves that stay small, never growing to become normal leaves, and they often remain around the base of the plant through the growing season. The presence of absence of the bud scales can be an identifying feature to distinguish between species of Primula, such as small forms of Primula denticulata (with bud-scales) and Primula atrodentata (without bud-scales).




Primula magellanica in autumn, leaves dying back and resting bud forming


Primula agleniana in spring, bud scales still surround the new leaves and flowers


Primula denticulata in late spring, bud scales lie flat as the growth point expands with new leaves and flowers

Bringing Seeds into Focus

Have you ever seen the book “Seeds:Time Capsules of Life” by Kesseler & Stuppy? It’s a gorgeous coffee table book of false-colored scanning electron microscope (SEM) images of seeds. These types of images can show wonderful detail at the microscopic level and give us more information to help distinguish between species. Primula seeds aren’t quite as fascinating as some of the seeds depicted in the book, but they do have minute details that make them interesting (see the SEM image above of a Primula seed that I false-colored ).  And though you can buy old scanning electron microscopes on ebay, this technique is out of reach for the majority. However, taking optical images of seeds can be done with minimal equipment, just as long as you are able produce magnification in the range up to 10X. This can be done with specialized lenses (like Canon’s MP-E 65mm), by reversing wide-angle lenses (like 24mm or 20mm) with a reversing ring (like Nikon’s BR-2A) or by attaching microscope lenses to the camera directly with an adapter (see this page on photomacrography.net). Or you can take images through a microscope using a camera adapter. If you want to add a scale to your image a micrometer slide is useful.

Focus slices

 

Primula brachystoma seeds focus stacked

The problem you encounter when taking magnified seed images is that the whole seed will not be in focus in a single image because of the narrow depth-of-field. In order to create an image with the whole subject in focus, we use a processing technique called "focus stacking". There are many good programs that do this as listed in the link, but I happen to use Zerene Stacker. This program combines the in-focus parts of multiple images taken with overlapping focus points to create an image that has the subject completely in focus.

So why would we want to look closely at Primula seeds?

A broken Primula agleniana seed attacked by fungus

Do you know what you area getting in a package of seeds? Even if you don't take an image of your seeds, looking at the seeds closely may reveal that there is more than one type of seed in a package, there is chaff or sand, or that some seeds are broken and molding. Keeping a images of your seeds allows you to compare with seeds that are supposed to be of the same species and can uncover misidentifications.

And it's really fun to uncover the hidden beauty of Primula seeds!

Leaf Venation in Primula

Venation is the arrangement of veins in a leaf. This arrangement can be a distinguishing characteristic of Primula.

Pinnate Venation is vein arrangement in a leaf with one main vein extending from the base to the tip of the leaf and smaller veins branching off the main vein. This is the most common arrangement in Primula.

Pinnate venation in P. blattariformis

Palmate venation is vein arrangement in a leaf with the principal veins radiate out from a single point, most commonly where the leafstalk/petiole ends, and diverges out toward the edge of the leaf. Only a few Primula species have this arrangement such as: P. latisecta, P. palmata, P. vaginata, P. septemloba, P. alsophila, and P. geraniifolia.


Palmate venation in P. palmata

The Yellow Cortusoides

Primula cortusoides is a pink flowered species which has a wide distribution from Western Europe through Siberia to Mongolia, North Korea and Northwestern China. It is the species which defines the Section Cortusoides, with plants efarinose, but having multicellular hairs, distinctly petiolate leaves, with a subrounded blade that is somewhat lobed at the margin and cordate at the base. The flowers are arranged in an umbel. In the wild it grows in a variety of habitats from rock crevices to slopes to woodland forests in low to mid altitudes. It is quite common in cultivation, however the yellow Cortusoides species are more of a mystery. These species are: P. eugeniae, P. pskemensis, P. pauliana and P. pelargoniifolia.



Primula eugeniae has a very small distribution centered in Northwestern Kyrgyzstan (Ferghana and Chatkal mountains) and does not seem to have been in cultivation though it looks to be very attractive. The flowers are a soft, pale yellow and the leaves are larger and more rounded but otherwise it superficially resembles P. cortusoides. This species grows in rock crevices at higher altitudes.

Primula pskemensis was described in 2004 from the Pskemense range of western Kyrgyzstan. It is very close to P. eugeniae but differs in the glandular, pubescent calyx and smaller flowers.

Primula pauliana is abnormal in form from other species in this section by having flowers arranged in a raceme (spike). It grows in SW Sichuan and North Yunnan in a variety of habitats from meadows to rock crevices to woodland at low to mid altitudes. Image courtesy Royal Botanic Garden Edinburgh.

Primula pelargoniifolia was described in 2014 from one locality in Qijiang, SW Chongqing. Its flowers are small and arranged in 2-4 superimposed umbels (whorls) and it grows in humid crevices and soil derived from red sandstone at low altitude. Image from the original description.

Spring 2015 Speaking Dates

Pam Eveleigh will be speaking at:

1. Calgary Rock & Alpine Garden Society on Thursday, March 12th, 2015 at 7:30pm. Venue is Lakeview Community Association Hall 6110 - 34 Street SW, Calgary, Alberta.

2. The B.C. Primula Group & the Alpine Garden Club of B.C.
on Saturday, April 25th, 2015 at 1:30pm. Venue is Van Dusen Cedar Room, Van Dusen Botanical Gardens, 5251 Oak Street, Vancouver, BC

3. The Vancouver Island Rock and Alpine Garden Society on Tuesday, April 28th, 2015 at 7:30pm. Venue is Gordon Head United Church, 4201 Tyndall Ave, Victoria, B.C.

Topic:  Modern Plant Hunting  How state of the art technology can be combined with information about historic quests to find plants. Pam will lead us through her personal experience of pursuing renowned people, places and plants to rediscover species not see in over a century. Her research has resulted in modifications to the Genus Primula.