Herbchronology

While leaves and stems of perennial herbs die down at the end of the growing season the root often persists for many years or even the entire life.

About two thirds of all perennial dicotyledonous herb species with a persistent root that grow in the strongly seasonal zone of the northern hemisphere show at least fairly clear annual growth rings.

[1] Counting of annual growth rings can be used to determine the age of a perennial herb similarly as it is done in trees using dendrochronology.

The term was introduced in the late 1990s,[5] however, the existence of annual rings in perennial herbs was already observed in earlier times by several researchers.

This may be relevant information to determine : Herbchronology allows to assess long-term annual growth rates of a perennial herbaceous plant without having to monitor it.

Root cross section (30 μm) of Penstemon venustus . Lignified tissue is stained reddish using Phloroglucinol/HCL. Black markers denote annual ring borders. Individual collected at the Wallowa Mts., Oregon, USA (2003)
Root cross section (30 μm) of Cirsium spinosissimum . Lignified tissue is stained reddish using Phloroglucinol/HCL. Black markers denote annual ring borders. Individual collected in the Churfirsten Mountain range, Switzerland (2002)
Root cross section (30 μm) of Silene vulgaris . Lignified tissue is stained reddish using Phloroglucinol/HCL. Black markers denote annual ring borders. Individual collected at Davos, Switzerland (2003)