19.3.3  Cryptophytes (geophytes): plants that grow from storage organs

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Cryptophytes (literally hidden plants) comprise major components of the understorey of nutrient-poor habitats such as the sandplains of southwestern Australia (Figure 19.8). Most are ‘wet-season active’, forming leafy shoots and reproductive organs during the assimilatory phase. With the advent of the following dry season they die back to a deeply buried corm, bulb or tuber. As with fire ephemerals (Section 19.3.2), limited nutrient resources are conserved extremely effectively, but in this case are withdrawn at the end of each growing season into newly formed storage organs rather than into seeds. Since fires are likely to occur only in the dry season, cryptophytes complete their life cyles by ‘avoiding fire in time and space’. As with fire ephemerals, cryptophytes benefit from the improved availability of light, moisture and nutrients in the seasons immediately following fire; indeed, some orchids and sundews flower predominantly after fire. Other cryptophytes reproduce vegetatively by forming tubers, corms or bulbs. In these species, prolific growth and rapid nutrient acquisition in the period following a fire provides bountiful reserves to be stored in below-ground organs.

In many ecosystems on impoverished soils (Chapter 16), a large proportion of total species are cryptophytes and other herbaceous perennials, with relatively few annual species present. Annuals have to establish from seed each season, often producing flower and setting seed only after a long juvenile phase. Productivity can be curtailed by short seasons and the imperative of absorbing sufficient nutrients from the soil over a short growing season. Cryptophytes, by contrast, carry over virtually complete stocks of nutrients and large amounts of energy-rich reserves from one season to the next through the agency of their underground storage organs, thus enabling leafy shoots, and in some cases flowers, to emerge almost immediately after rain opens a new season. Cryptophytes are also highly resilient to adverse seasons: in drought years, for example, individuals deplete reserves of dry matter and nutrients, and sometimes fail to reproduce effectively. Even in these cases, sufficient resources are carried over to the next season to allow a population to survive. If more favourable conditions then prevail, nutrient and energy stores are replenished to earlier levels.