The Age Structure and Life Table of Rare Eremophyte Helianthemum ordosicum Population Chemical constituents of Helianthemum ordosicum Nematicidal activity of extracts of Helianthemum ordosicum against Bursaphelenchus xylophilus A new species of Helianthemum Mill.(Cistaceae) Spectral Analysis of Dynamics of Rare Eremophyte Helianthemum ordosicum Population