Persepolium

Persepolium —indeterminate growth and accelerated flowering

Persepolium species are endemics to the Zagros Mountains in the South-West Iran. The Zagros has a cold, semi-arid climate (Bsk in Köppen classification system) with a snowy, cold winter and a mild rainy spring followed by a dry summer and autumn ( Frey & Probst 1986, Heshmati 2007). The southern part of the Zagros is dominated by a semiarid, dry steppe climate (Bsh in Köppen) ( Raziei 2017). Persepolium species inhabit sparse grass or forest-steppe communities at the elevations from 1000 to 3700 m a. s. l. (see also Yurtseva et al. 2017). Due to the short growing season, interrupted by long drought, the plants flower early in spring and complete fruiting before the onset of summer drought.

Persepolium species have a Type I shoot system formed by reproductive shoots with indeterminate growth, which maintain the apical shoot meristems in a vegetative state and produce more or fewer cymes in a thyrse, depending on the length of the growing season at different elevations. Their shoots are characterized by a short lifespan, extremely short innovation zones, and accelerated formation of long and intensively branched inflorescences. In intercalary thyrses, each cyme is supplied by a well developed subtending leaf. Far spaced cymes alternate with paracladia in no particular order, so the thyrses are weakly integrated. The inconspicuous, greenish-purple perianths indicate self- or fly-pollination (see also Yurtseva et al. 2017). By retaining very short innovation zones in the perennial axial system, P. aridum View in CoL and P. dumosum View in CoL exist as semi-shrubs; P. khajeh-jamalii has thyrses in terminal positions and longer innovation zones of reproductive shoots, but it is a dwarf semi-shrub. P. salicornioides View in CoL and P. spinosum View in CoL retain the thickened, lignified axes of their reproductive shoots for over a year, existing as dwarf shrubs ( Yurtseva et al. 2016a: Supplementum 11, Yurtseva et al. 2017).