The Persian Ironwood of the Grete-Rehor-Park

This tree is twice as wide as it is tall. The Persian ironwood on Schmerlingplatz stands between 6 and 10 metres high and throws a crown 16 to 18 metres across, which is what the species does when nobody crowds it: instead of a trunk it grows a low fused knot of leaning stems that peel in grey, green and fawn plates like a plane tree's, then spreads sideways until it makes its own room. The city measures the base at 460 centimetres around, an exceptional figure for a species most European gardens never get past arm's width. Vienna protected it on 5 November 1956, and the stated reason was not its age or size but simply its rarity. Parrotia persica grows wild only in the Caspian forests of northern Iran and Azerbaijan, and in the 1950s a full-grown one in a Vienna square was worth a legal decree. What it does in late October is the reason to walk over. The leaves do not turn a single colour, they turn several at once and unevenly, so one branch goes scarlet while the next is still green and a third has already reached amber, and the whole low dome ends up looking backlit even under grey sky. The small park around it, a wedge of grass beside the Justizpalast, was named in 2016 after Grete Rehor, the first woman to hold a ministry in Austria.