Aspilia montevidensis (Spreng.) is an herbaceous perenium plant native of South and Southeast regions of Brazil, where it is considered a weed. Very few studies with this species have been conducted, especially on its phenology. The objective of this study was to determine the base temperature and the rural accumulation of some growth stages for A. montevidensis. The experiment was carried out in Santa Maria, Rio Grande do Sul State Brazil, with six planting dates (20/12/2005, 14/2/2006, 6/3/2006, 4/4/2006, 5/5/2006, and 8/6/2006) and seven positions on plant stems. The experimental design was completely randomized and the experimental unit was one plant grown in pots filled with commercial substratum. The dates of the developmental stages transplanting (T), visible buds (VB), open capitulum (OC) and senescent capitulum (SC) were measured on the main stem and on first and secondary lateral branches. The base temperatures were estimated for the stages T-VB and VB-SC using three methods, for the estimative of the duration, in ºC day, of the T-VB, VB-OC and OC-SC stages. The daily thermal accumulations were calculated from transplanting stage. The estimated base temperature for the T-VB and VB-SC stages phases were 13ºC e 7ºC, respectively. The duration, in ºC day, of the T-VB stage varied among stems and planting dates, with the shortest duration of 489.1 and the longest duration of 1269.4 ºC day. The duration, in ºC day, of VB-OC and OC-SC, in general did not vary among stems and planting dates, being around 179.8 and 97.2 ºC day, respectively.
Phenology; degree-days; ornamental plant; weed plant; yellow calendula
