I was curious about Tienchi Flower tea; the internet didn't provide as much information as I expected, but along with some dubious results (one of which spoofed a malware attack with piercing beeps and a warning to contact my ISP) were several sites about "the most expensive teas in the world." Easy enough to imagine writer Jason Tracey googling that topic to find a character detail for Morland (though of course I must then wonder how it is that Joan knows the tea too - by the tin? Or did Sherlock assign her olfactory exercises along with single stick and Bentham reading? I wouldn't guess its scent would be as noticeable as fermented shark meat.) That the tea is often ascribed cooling and calming properties adds a nice thematic element.
Further searching identified several alternate transliterations (including sanqi, sanchi, tian qi, tien chi) as well as the western scientific name for the plant, Panax notoginseng.
While tea from the flowers has clinically verified anti-inflammatory and anti-insomnia properties, the plant's root is more widely used and studied in a range of medical contexts.
However, one other as yet undocumented effect of tienchi flower is on the tea cozy.
First, here's a screen cap from the "you go, I go" scene in 4x01, showing the familiar red & green knit tea cozy they've had since the start.
Next, here's a screen cap from the kitchen conversation between father and son in 4x02, after the absence of tienchi flower has been discussed. Not only no tienchi flower, but no teapot or cozy at all.
And finally, a cap from later in 4x02, when Sherlock makes tienchi flower tea and tells Watson he Wants To Believe his father is making amends. We see a dramatic, even ominous, change in prop, the frumpy old cozy suddenly replaced by a dark, tailored, and one might say overbearing stuffed-envelope of heat containment. Perhaps it arrived on a plume of black smoke...?
