Exactly which kind of cardamom should I use in pho (phở)? I have been cooking pho for a while. Pho recipes differ from one another, but one of the most common spice ingredients is cardamom. Having looked at various sources, recipes, and Wiki pages, I feel more confused than ever. Some insist that green cardamom should be used in pho, which is also what I myself have been using to cook pho. For example this recipe apparently uses green cardamom.

However, a whole lot of pages point to black cardamom. The problem is that it seems what is known as "black cardamom" is not monolithic but an umbrella term for two similar spices. According to its Wikipedia page:


  At least two distinct species of black cardamom occur: Amomum subulatum (also known as Nepal cardamom) and Amomum tsao-ko. The pods of A. subulatum, used primarily in the cuisines of India and certain regional cuisines of Pakistan, are the smaller of the two, while the larger pods of A. tsao-ko (Chinese: wiktionary:草果; pinyin: cǎoguǒ; Vietnamese: thảo quả) are used in Chinese cuisine, particularly that of Sichuan, and Vietnamese cuisine.


In another section of the same page:


  The pods are often used in Vietnam, where they are called thảo quả and used as an ingredient in the broth for the noodle soup called phở.


So I gather from this page that it should be tsao ko that goes in pho.

But I still have doubts. I happen to have tsao ko, a lot of it, and it is something I use quite frequently in other Asian dishes. It looks similar to the black cardamom in a lot of pictures on recipe sites, but not quite the same. Examined closely enough, tsao ko is round, fleshy, plump, and looks like this:

 

In contrast, the black cardamom shown in pho recipe photos and most commonly available is leaner, pointier:

 

I think it is very obvious they are different things and the latter is apparently the other black cardamom, Amomum subulatum. A pho recipe site links to this Amazon page. It seems what is sold as "black cardamom" is most likely Amomum subulatum.

So here are my questions: What is pho in Vietnam cooked with? Is it a divided matter, a matter of preference? Is green cardamom used at all? If black cardamom is the way to go, which black cardamom?
In phở soup, we use thảo quả, or Lanxangia tsao-ko, formerly known as Amomum tsaoko. Thảo quả trees are grown in Northern Vietnam, Laos, and in Yunnam China (known as 草果).
We call Black cardamom (Amomum subulatum) as đậu khấu thơm. Black cardamom trees are grown in India, Nepal, Burma, Tibet, Yunnam. Black cardamom trees are not native to Vietnam, and their pods are not used in phở traditonally.
We call green cardamom (Elettaria cardamomum) as bạch đậu khấu. Like black cardamom, it's not used in phở, either.