**3. Final comments**

should be scattered sparsely on the surface and pressed firmly into the soil, burying them no further than 0.3-cm deep. Soil needs to be moist to saturation. Seed does not require stratifi‐ cation and germinates in less than 2 weeks. When plants get enough size, they must be transplanted [21]. *Colocasia esculenta* germ plasm can be conserved as seed for at least 2 years at constant 5°C and −20°C when seed moisture content is reduced to 10–12% and at ambien‐ tal room temperature (21.5–34.4°C, mean 27.2°C) when seed moisture content is reduced to 7.3% [57]. *Canna indica* is an herbaceous species with ornamental and medicinal value, having seeds with a hard seed coat. Seed germination is good at 10–40°C, being the optimal temper‐ ature range between 13.84 and 34.41°C, determined by the enthalpy of activation [58]. To open the imbibition lid, a raised incubation temperature of 50°C during 24 hours in wet surround‐ ings is enough. This hydration induces germination. As a result, the integumentary part of the seed coat softens, making it possible forthe germinalroot to emerge from the seed. This waterregulating mechanism, combining an impermeable palisade layer and imbibition lid, is a unique feature of the Cannaceae. The seed coat is mainly of chalazal origin, and the main mechanical layeris formed by the exotesta. Otherfamilies of the Zingiberales, in contrast, open by an operculum formed by all seed coat layers. Moreover, the seed coat in those families is of integumentary origin, and the main mechanical layer is formed by the exo- and/or endo‐ testa [59]. *Heliconia rostrata* seed germination is well known as difficult and problematic, because the embryo is not yet well differenced when the seed matures, and it has a hard testa which does not allow waterto get into it. It can take from 3 months to 3 years [60]. *Iris versicolor* seeds germinate 58% in the greenhouse using cold stratification; this is storing seeds in wet paper towels at 4–5°C for 3–4 weeks [61]. *Iris pseudacorus* germinates 80–86% in an incubator at 12-h/12-h light regime and 30/20°C alternating temperatures or constant temperature of 26°C. In the latter case, seeds must be pretreated by immersion in 10% Domestos solution for 5 min and then imbibed on 1% agar for 8 weeks at 6°C, and then the seed is scarified (covering structure removed and seed coat chipped). After that, a solution of 250-mg/l

194 New Challenges in Seed Biology - Basic and Translational Research Driving Seed Technology

gibberellic acid (GA3) must be added to the 1% agar medium.

We have included here species as *Asclepias incarnata, Hibiscus moscheutos, Filipendula ulmaria, Liatris pycnostachya, Lobelia cardinalis, Lythrum salicaria, Mentha spicata, Rudbeckia hirta* and *Silphium perfoliatum* [1] that have been tested in Ohio, Kentucky and Minnesota (USA).

To germinate *Asclepias incarnate* seeds, they must be placed into plastic bags filled with moist perlite or vermiculite and stored for 4–12 weeks in a cold (1–3°C) place. Good germination results have been reported without stratification by soaking the seed twice in 87°C for 12 hours. Germination trays can also be used, filling the cells with a commercial seedling mixture or a mix of *Sphagnum* peat moss and vermiculite and moistening them very well. Seeds should be gently pressed into the soil, three seeds per cell, and covered with a very thin layer of soil. It is recommended to keep the soil moist during germination by spraying or misting. Ambient temperatures should remain between 18 and 23°C. This species requires light for germination [21]. *Filipendula ulmaria* is successfully germinated (95%) using 1% agar as germination substrate and incubator conditions of 25/10°C, 8 h/16 h, or 23/9°C, 12 h/12 h

**2.11. Megaforbics and other groups**

Seed technology for multiplication helophytes needs further experimental work. Significant efforts have been done, but it is a challenge to have a set of available information ready to be transferred to the productive sectors that are interested in this type of plants. Plants used in constructed wetlands with horizontal subsurface flow have a promising future as sustaina‐ ble elements of the upcoming sewage equipment. For this reason improvements on the biotechnology of these species are a worthwhile researching line, where seed technology can play an important role.
