Hepatica: Pollination, seeds & germination

Pollination, Seeds & Germination

Hepatica species are the true spring harbingers of eastern North American woodlands. Their cheerful, bright flowers are the first to dot the forest floors in many parts of eastern North America, starting early to mid-April. At that time, usually the weather is still cold and frequent rains are possible. This raises the question of the pollination.

One study that looked at Hepatica pollination ecology showed that Hepatica americana flowers are in large proportion autogamous (self-pollinated) (1); a very good idea that other early spring flowering species have as well.

Various early spring pollinators – if present/active – have been observed visiting Hepatica americana flowers. These are mainly solitary bees and dipteras looking for nectar, which is absent in Hepatica flowers, but in the absence of other more rewarding species, they will visit only to gather pollen. Hepatica flowers are protogynous (their female parts mature before the anthers), and thus outcrossing becomes also possible. In any case, the cold weather of early spring in our region will often hinder the foraging of insects.

Another article concluded that Hepatica acutiloba relies more heavily on pollen from other blooming plants for good seeds set, meaning more insects visits (2).
While this might have been possible for the particular population taken into account, it contradicts the situation of SW Ontario where H. acutiloba may flower about 2 weeks earlier than H. americana(!),  when the chance of early pollinators is even greater reduced by the cold weather.

One study carried on a northern population of H. acutiloba over a few years (3) showed that the only active pollinator at that time was Asclera ruficollis, which was recorded moving for very short distances between Hepatica flowers. This accounted for a lower seeds set, but it also means a lower level of outcrossing as well.

For those unfamiliar with some of the terms, the conclusion is that in many cases the seedlings will display the traits of the parents (seeds from self-pollinated flowers) – which is good news when propagating from seeds the special forms!
However, taking into account the possibility of outcrossing, there is also a chance that a proportion of seeds will produce seedlings with different traits than the parent.
So, it is good to keep in mind that when growing Hepatica from seeds, the seedlings may not come true with the mother-plants.

 

Moving forward:

What we routinely call seeds are actually fruits – achenes, formed in rounded heads which at the time of maturity are still green looking. They are equipped with elaiosomes which attract ants, which will help in the dispersal of the ‘seeds’ (myrmecochory).
When the ‘seeds’ are close to maturity, the pedicels gradually bend down under the weight of the fruit heads, hiding under the new leaves. This makes them hard to spot and is a good sign to keep in mind that the collecting has to be done soon.

The seeds are ready to collect in SW Ontario somewhere in late May/June, depending when the flowering begun. Collecting the ‘seeds’ – must be done at the right time, otherwise they fell down and are carried away by ants (mostly). On the other hand, they cannot be forcefully detached, they have to mature properly. The proper moment is when they fell by themselves at a light touch.

To ease the process is best to enclose the fruit heads in small muslin/organza bags which will retain the seeds. Even this not always gives 100% guarantee for seeds, especially if there is a determined chipmunk in the garden (they are known to enjoy the fruit heads).

All in all, collecting Hepatica ‘seeds’ in the wild (and in the garden) is not an easy job, to say the least…

Handling and SOWING the Hepatica seeds

Like many other Ranunculaceae, at the time of maturity, the seeds contain immature embryos and are hydrophilic – they need to be sown right away or kept moist at all time and allowed a warm/slightly warm period  followed by a cold period for germination. It has been shown that the embryos will start growing rapidly actually at the end of summer when the day/night temperatures start to decline. So they also respond to the variations in temperatures.

For all living in the Northern Hemisphere, ‘warm’ simply means: keep the sowing pots outdoors, in a shaded place, and let them follow the natural variations in temperature until winter arrives (keep the pots out of heavy rains; a shaded spot along the house under eaves, under a patio table, underneath a large shrub, or anything similar, be creative…..). Even a tight mesh placed over the seeds tray will work well (but don’t forget to check the moisture!).

By sowing the seeds right away (in June), they will undergo naturally the required warm/ cold (winter) periods and start germinating in the spring (March-April).

Sometimes even when sown fresh/moist stored, the embryos may not reach the size allowing for germination after the cold cycle (first winter). In this case, the seeds require one more warm/cold cycle for germination, ie. germination in the second spring after sowing. Also, it seems that in some rare cases the seeds can germinate in the third year!

The seeds can also be stored in slightly moist vermiculite at warm until fall, to be sown at other times throughout the summer/fall/ – be advised that it will take trail and error until one gets used with storing them moist. If you collect your own seeds, it is best to sow them right away and keep the pots/trays covered with a mesh in a shaded location.

Seeds which were kept dry for a few months will still germinate, but in the second year and in lower proportion.

Depending on the seeds provenience/population, some seeds will definitely germinate only in the second year after sowing – even if kept moist at all time! This can be noticed in the picture below; newly germinated seedlings, close to one-year old. Always keep your pots for at least 2 (3) years!

During moist storage in vermiculite (and most likely in the soil as well), the seeds will undergo a transition.  From the fresh green/yellowish color when collected they will slowly become brown then black . It is the normal transition of the outer teguments during maturation. Also, at this stage, the white elaiosomes are not visible anymore (their only function being to attract the ants which disperse the fresh seeds).

In most cases the seeds will start to germinate in late March/April (in our climate) and the seedlings remain small in the first season. It is best to grow them in the same pot for at least one more year and transplant them in the second or third year. Actually the roots are formed during late winter/very early spring, before the shoots emergence in late spring.

The seeds and behaviour/treatments for germination of other Hepatica species, like transsilvanica, japonica, henryi…, are the same. In the picture below, a pot with Hepatica japonica where new seedlings are appearing right now (2018), close to last years seedlings (all sown in 2016). This illustrates well what I mentioned about germination happening sometimes over a 2 years period.

After few years of sowing Hepatica seeds I can add that Hepatica acutiloba seems to germinate more easily and grow faster than H. americana. So, for the beginners I recommend to start growing from seeds with a H. acutiloba form, especially from the ‘pastel mix’ population, which has an excellent germination.

H. nobilis is also a good germinator and grower, while H. transsilvanica has been the slowest to flower for me, from all species grown to date (from seeds).

I try to update this page once in a while. For now, I hope this provides a good, summarized info for those wanting to collect their own/start Hepatica from seeds.
I also recommend to read the following post before trying to purchase seeds:
Hepatica acutiloba and a checklist for growing from seeds

Please follow with the next page: Transplanting and caring for the seedlings.

1 – Autogamy and Competition for Pollinators in Hepatica americana (Ranunculaceae): Alexander F. Motten, American Journal of Botany, Vol. 69, No. 8 (Sep., 1982), pp. 1296-1305
https://www.jstor.org/stable/2442754?seq=1#page_scan_tab_contents

2 – The Pollination Ecology of Hepatica acutiloba DC. (Ranunculaceae): Peter Bernhardt, Bulletin of the Torrey Botanical Club, Vol. 103, No. 6 (Nov. – Dec., 1976), pp. 255-258
https://www.jstor.org/stable/2484189?seq=1#page_scan_tab_contents

3 – Pollen limitation in a northern population of Hepatica acutiloba: Stepehn D. Murphy, L. Vasseur, Canadian Journal of Botany 73(8):1234-1241, Feb. 2011
https://www.researchgate.net/publication/237165534_Pollen_limitation_in_a_northern_population_of_Hepatica_acutiloba